Fixation by ion exchange of toxic materials in a glass matrix

ABSTRACT

This invention relates to the immobilization of toxic, e.g., radioactive, materials in a silicate glass or silica gel matrix for extremely long periods of time. Toxic materials, such as radioactive wastes containing radioactive cations, which may be in the form of liquids, or solids dissolved or dispersed in liquids or gases, are incorporated into a glass or silica gel matrix, having alkali metal, Group Ib metal and/or ammonium cations bonded to silicon atoms of said glass or silica gel through divalent oxygen linkages, by a process which involves the ion exchange of said toxic or radioactive cations with said alkali metal, Group Ib metal and/or ammonium cations to bind said toxic or radioactive cations to silicon atoms of said glass or silica gel through said silicon-bonded divalent oxygen linkages. Thereafter, the resulting glass or silica gel now characterized by toxic or radioactive cations bonded to silicon atoms through divalent oxygen linkages can be stored, or packaged in suitable containers, or disposed of as by burial, and/or sintered to collapse the pores thereof.

RELATED APPLICATIONS

This application is a continuation of our co-pending application U.S.Ser. No. 039,595, filed May 16, 1979, now abandoned, entitled FIXATIONBY ION EXCHANGE OF TOXIC MATERIALS IN A GLASS MATRIX, which in turn is acontinuation-in-part of our application U.S. Ser. No. 959,222, filedNov. 9, 1978, now abandoned, entitled: FIXATION BY ION EXCHANGE OF TOXICMATERIALS IN A GLASS MATRIX, now abandoned.

BACKGROUND OF THE INVENTION

The disposal of large quantities of toxic materials such as high levelradioactive wastes stored in spent reactor storage pools, or generatedin the reprocessing of spent nuclear power reactor fuel, or generated inthe operation and maintenance of nuclear power plants, is a problem ofconsiderable importance to the utilization of nuclear power. It isgenerally accepted that the most promising approach is to convert theseradioactive wastes to a dry solid form which would render such wasteschemically, thermally and radiolytically stable.

The problem of dry solid stability of radioactive wastes is closelyrelated to the safety of human life on earth for a period of more than20,000 years. For example, radioactive wastes usually contain theisotopes Sr⁹⁰, Pu²³⁹, and Cs¹³⁷ whose half lives are 28 years, 24,000years, and 30 years, respectively. These isotopes alone pose asignificant threat to life and must be put into a dry, solid form whichis stable for thousands of years. The solid radioactive waste form mustbe able to keep the radioactive isotopes immobilized for this length oftime, preferably even in the presence of an aqueous environment. Theradioactive wastes are produced in high volumes and contain long-lived,intermediate-lived, and short-lived radioactive ions and somenon-radioactive ions. These solutions can be highly corrosive and it isdifficult, if not impractical, to reduce them to concentrated forms forfurther processing or storage.

The two most popular types of commercial reactors both of which producelow level wastes are the Boiling Water Reactor (B.W.R.) and thePressurized Water Reactor (P.W.R.). In a typical Pressurized WaterReactor (P.W.R.), pressurized light water circulates through the reactorcore (heat source) to an external heat sink (steam generator). In thesteam generator, where primary and secondary fluids are separated byimpervious surfaces to prevent contamination, heat is transferred fromthe pressurized primary coolant to secondary coolant water to form steamfor driving turbines to generate electricity. In a typical Boiling WaterReactor (B.W.R.), light water circulates through the reactor core (heatsource) where it boils to form steam that passes to an external heatsink (turbine and condenser). In both reactor types, the primary coolantfrom the heat sink is purified and recycled to the heat source.

The primary coolant and dissolved impurities are activated by neutroninteractions. Materials enter the primary coolant through corrosion ofthe fuel elements, reactor vessel, piping, and equipment. Activation ofthese corrosion products adds radioactive nuclides to the primarycoolant. Corrosion inhibitors, such as lithium, are added to the reactorwater. A chemical shim, boron, is added to the primary coolant of mostP.W.R.'s for reactivity control. These chemicals are activated and addradionuclides to the primary coolant. Fission products diffuse or leakfrom fuel elements and add nuclides to the primary coolant. Radioactivematerials from all these sources are transported around the system andappear in other parts of the plant through leaks and vents as well as inthe effluent streams from processes used to treat the primary coolant.Gaseous and liquid radioactive wastes (radwaste) are processed withinthe plant to reduce the radioactive nuclides that will be released tothe atmosphere and to bodies of water under controlled and monitoredconditions in accordance with federal regulations.

The principal methods or unit operations used in the treatment of liquidradwaste at nuclear power plants are filtration, ion exchange, andevaporation.

Liquid radwastes in a P.W.R. are generally segregated into fivecategories according to their physical and chemical properties asfollows:

a. Clean Waste includes liquids which are primarily controlled releasesand leaks from the primary coolant loop and associated equipment. Theseare liquids of low solids content which are treated in the reactorcoolant treatment system.

b. Dirty or Miscellaneous Waste includes liquids which are collectedfrom the containment building, auxiliary building, and chemicallaboratory; regeneration solutions from ion-exchange beds; and solutionsof high electrical conductivity and high solids content frommiscellaneous sources.

c. Steam Generator Blowdown Waste is condensate from the steam that isremoved (blowdown) periodically to prevent excessive solids buildup.

d. Turbine Building Drain Waste is leakage from the secondary systemthat is collected in the turbine building floor sump.

e. Detergent Waste includes liquids from the laundry, personneldecontamination showers, and equipment decontamination.

Liquid radwastes in a B.W.R. are generally segregated into fourcategories according to their physical and chemical properties asfollows:

a. High-Purity Waste includes liquids of low electrical conductivity(<50 μmho/cm) and low solids content, i.e., reactor coolant water thathas leaked from the primary reactor system equipment, the drywell floordrain, condensate demineralizer backwash, and other sources ofhigh-quality water.

b. Low-Purity Waste includes liquids of electrical conductivity inexcess of 50 μmho/cm and generally less than 100 μmho/cm; i.e.,primarily water from floor drains.

c. Chemical Waste includes solutions of caustic and sulfuric acid whichare used to regenerate ion exchange resins as well as solutions fromlaboratory drains and equipment decontamination.

d. Detergent Waste includes liquids from the laundry and personneldecontamination showers.

The liquid radwastes from both types of reactors are highly dilutesolutions of radioactive cations, and other dissolved radioactivematerials as well as undissolved radioactive particles or finely dividedsolids.

A practical process for disposing of radioactive materials in a drysolids form having high resistance to leaching and other forms ofchemical attack would not only be suitable for the disposal ofradioactive nuclear wastes, but also for the fabrication of radioactivesources useful in industry, medicine, and in the laboratory.

Heretofore, there did not exist any practical, foolproof means for thesafe disposal, storage and immobilization of pernicious radioactivewaste material. Present day storage containers do not provide sufficientisolation and immobilization of such radioactive material, sufficientlong-term resistance to chemical attack by the surroundings, andsufficient stability at high temperature.

Currently low level radioactive waste, that is radioactive wastegenerated at reactor sites, is disposed of in the following manner:

(A) The dead ion exchange resin containing radioactive waste is mixedwith cement and cast in forty gallon barrels.

(B) The bottoms from evaporators which contain the radioactivecontaminated boric acid and the solutions used to regenerate the ionexchange columns are mixed with cement powder and cast in forty gallonbarrels.

(C) The filters containing particulate forms of radioactive waste areusually encased in cement in barrels.

These cement barrels are transported to low level radioactive wastesites and buried six feet deep in the ground. At least one of the sitesis in the United States Eastern States and exposed to substantialrainfall. In Europe, these barrels are buried at sea. In both caseswater will first corrode the metal then the cement and will relativelyquickly expose the radioactive ions for leaching into the ground wateror sea water. Because the U.S. burials are only a few feet deep, thecontaminated water can readily intermix with streams, lakes and rivers,thus, entering the ecosphere. The rationale for this practice is theassumption that upon sufficient dilution the radioactivity becomesharmless.

Some of the most serious nuclear wastes are cesium and strontium whichare biologically similar to sodium and calcium. They have thirty yearhalf lives indicating that they should be isolated from the exospherefor at least three hundred years (ten half lives). At Bikini, theexperts assumed that dilution had made the island inhabitable afterdecades in which no atomic explosions were performed, yet when thepopulation was returned to the island its health was deleteriouslyeffected. It has since been realized that plants and animal lifebiologically reconcentrate these radioactive elements back up todangerous levels.

Thus, the "safe" concentration of radioactive waste must be much lowerthan accepted values and a more durable substitute for cement is needed.In one aspect, the present invention presents a safe alternative to thecement-solidification of low level waste.

Another route heretofore suggested is the so-called dry solids approachwhich involves the fixation of the waste materials in glasses via mixingwith glass-forming compositions and melting to form glasses. Thisapproach offers some improvement regarding isolation and decrease in therate of release of radioactive elements when the outer envelopes orcontainers are destroyed. Further, such glasses remain relatively morestable at high temperatures than plastic and are generally morechemically durable in saline solutions than are metals. Glasses withhigh chemical durability and low alkali ion conductivity suitable forthis prior art technique are formed at very high temperatures, e.g.,1800° C. and higher. Prior processes utilizing such high meltingglass-forming compositions are economically unsound and moreover, causea dangerous problem due to the risk of volatilization of perniciousradioactive materials. Furthermore, this procedure is restricted to drysolid radioactive wastes and provides no solution to the high volumes ofliquid radioactive wastes produced by the operations and maintenance ofnuclear reactors, by the current practice of storing spent fuels inpools of water, and by spent reactor fuel recovery systems.

In view of the overall difficulties of handling radioactive material,and especially in view of the danger of volatilization of radioactivematerial into the atmosphere, attention has been directed to using glasscompositions having relatively low melting temperatures, that is to say,using glass compositions with SiO₂ contents as low as 27 weight percent.While the problem of volatilization of radioactive materials is reduced,it is not completely controlled. Moreover, the resultant glasscomposition exhibits greatly reduced chemical durability and increasedion diffusion rates for the radioactive materials present therein. Thegreater this diffusion rate, the lower is the ability of the glass tokeep the radioactive materials immobilized in its matrix. For long-termcontainment of radioactive waste, demanded under present day standard,these prior glass compositions are inadequate.

U.S. Pat. No. 3,640,888 teaches the production of neutron sources byencapsulating californium-252 in glass using the steps of packing anopen-ended vitreous tube a porous powder of quartz having an organicliquid ion exchange material sorbed thereon, passing an aqueous solutioncontaining californium-252 cation through the powdered quartz, dryingand heating the powdered quartz and tube in air to oxidize andvolatilize the organic liquid ion exchange material resulting in thenon-volatile oxide of californium-252, and then fusing the tip andpowder contents to form a vitreous body containing the californium-252oxide. The patent, however, does not disclose, teach or suggest the useof porous glass containing silicon-bonded cation-oxy groups which areexchangeable by radioactive cations in aqueous solution nor does itdisclose or suggest any method or technique for concentrating and safelydisposing of radioactive wastes.

U.S. Pat. No. 1,533,794 teaches the packaging of radium emanations in aglass capillary tube followed by sealing the ends of the tube and thusenclose emanations previously introduced into the tube. There is noteaching, however, of any method for concentrating and/or immobilizingradwaste.

U.S. Pat. Nos. 2,336,227; 2,340,013; 2,522,524; 3,364,148 and 4,083,579relate to the treatment of porous glass with non-radioactive ions(radioactive ions in the case of 3,364,148) followed by heating to closethe pores which contain the ions. U.S. Pat. Nos. 3,147,225 disclosesrefractory particles, which contain no or minor amounts of silica andpreferably are crystalline, within which particles a specificallyselected radioactive cation is firmly fixed for use in self-luminousmarkers, liquid level indicators and other applications. There is nodisclosure or suggestion in any of these patents, however, of reacting asilicate glass or silica gel having silicon-bonded alkali metal oxy,Group Ib metal cation oxy and/or ammonium cation oxy groups withradioactive wastes which typically are complex mixtures of radioactiveand non-radioactive compounds and/or ions nor is there any disclosure ofprocedures for treating radioactive wastes.

U.S. Pat. No. 3,116,131 discloses the method of binding expanded silicaparticles with a binder and shaping and curing into a desired form,followed by impregnation with a solid desiccant, e.g., sodium hydroxide,and followed by impregnation with a radioactive gas and steam to absorbthe water vapor followed by capillary condensation thereby entrainingthe radioactive gas in the pores after which the pores are closed byheating. The patent fails to disclose the chemical combination of wasteradioactive ions in the pores of a porous glass or silica gel by ionexchange followed by closing the pores to provide the dual security ofchemical combination and mechanical entrapment of the radioactive ionsin the glass.

U.S. Pat. No. 3,959,172 discloses the method of forming and reacting amixture of silicate or other source of silicon, a radionuclide waste anda metal cation to produce complex metalosilicate crystals which entrapthe radionuclide waste. U.S. Pat. Nos. 3,451,940 and 3,849,330 disclosethe utilization of a thermite reaction to form a complex polysilicateproduct containing the radioactive wastes. None of these patents teachor suggest the use of porous glass or silica gel which is characterizedby an interconnecting porous structure of high ion-exchange capabilitysuch that upon contact with pernicious liquid radwaste the radioactivespecies (cations, for the most part) thereof become "ion-exchanged" tothe glass or silica gel, and/or followed by treating to collapse theporous structure thereof to immobilize such radioactive species.

U.S. Pat. No. 3,167,504 discloses the purification of radioactive wasteliquid by absorption on a synthetic zeolite which is then sealed in asuitable container for burial. There is no disclosure of the porousglass or silica gel discussed previously and/or of heating to collapsethe pores of a porous glass or silica gel around radioactive materials.

U.S. Pat. Nos. 3,114,716; 3,262,885; 3,365,578 and 4,020,004 each dealwith various techniques involving the preparation of glass-formingmixtures followed by firing to form a glass and none of them disclosethe impregnation of a porous glass or silica gel with radioactive wasteswhereby the radioactive species thereof become chemically bonded to theporous glass or silica gel followed by heating to collapse the pores.

U.S. Pat. No. 3,093,593 discloses methods for disposing of radioactivewastes by forming a porous ceramic piece from clays and other silicatesfollowed by prefiring such pieces to destroy ion exchange capacity andthereafter impregnating the prefired pieces with radioactive liquidwastes. The pieces saturated with radioactive waste are then heated tovitrify them and render them non-absorptive. This patent teaches awayfrom our invention which relies on ion exchange for strongly binding theradioactive waste in the pores of a glass or silica gel.

U.S. Pat. No. 3,938,974 relates to glass, optical wave guide fibers andtheir production. Radioactive materials cannot be used in such fibersbecause they form color centers which absorb light. Not only does thispatent fail to disclose the use of radioactive materials, the presenceof such materials are inimical to the express objects of the patent.

Two articles, The Behavior of Silica Gel Towards Certain Aklalies andSalts in Aqueous Solution by W. A. Patrick and E. H. Barclay, J. Phys.Chem., Volume 29, page 1400, 1925, and Interaction of Metal Silica GelsWith Aqueous Electrolyte Solutions by L. V. Ponomareva, A. P. Dushinaand V. B. Aleskovskii, Zhurnal Prikladnoi Khimii, Vol. 48, No. 10, pp.2150-2155, 1975 relate to the ion exchange of alkali metal cations in asilica gel with heavy metal cations. However, neither of these articlesare concerned with methods to remove radioactive species fromradioactive waste streams by impregnating porous glass or silica gelwith such streams, followed by heating to collapse the pores.

As will be apparent hereinafter from the various aspects of applicant'scontributions to the art, there are provided novel methods to obtainnovel compositions and articles for the containment of pernicious anddangerous radioactive materials over extraordinarily long periods oftime. Unlike melting glass containment procedures, the methods of theinvention need not involve any steps which would expose radioactivematerial to high temperatures, e.g., above about 900° C., therebyeliminating the environmental hazard due to possible volatilization ofradioactive material into the atmosphere.

Belgian Pat. No. 839,705, issued July 16, 1976 and GermanOffenlegungsschrift No. 2,611,495, published July 10, 1976 correspondsubstantially to U.S. Pat. No. 4,110,096, issued Aug. 29, 1978 to PedroB. Macedo named as an inventor herein and Theodore A. Litovitz. Thesepatents and Offenlegungsschrift contain essentially the same disclosuresbut there is no disclosure of porous glass forms having sufficient ionexchange capabilities to bind practical amounts of radioactive cationsto the glass to thereby concentrate and contain said radioactive cationsin the manner taught herein. Although mention is made of removing silicagel, that may have deposited in the pores of the porous glass during itsmanufacture, by washing with sodium hydroxide, it has been found thatprocedures for doing so known in the art fail to produce sufficientamounts of silicon-bonded sodium oxy (ion exchange) groups needed forproviding the binding of practical levels of radioactive cations fromthe radwaste. Furthermore, the presence of silica gel in the pores canbe advantageous in this invention as providing more surface area and ahigher proportion of silicon-bonded hydroxyl groups and ultimatelyhigher amounts of silicon-bonded metal oxy or ammonium oxy groups forion exchange with radioactive cations.

SUMMARY OF THE INVENTION

The invention relates to the concentration and immobilization of toxiccations, such as, Hg⁺⁺, Hg⁺, Cd⁺⁺, Tl⁺, Pb⁺⁺, radioactive cations, andthe like for extremely long periods of time.

In one aspect, the invention contemplates novel sintered silicate glass(preferred) or silica gel compositions or articles having high chemicaldurability to aqueous corrosion and having sufficiently low radioisotopediffusion coefficient values to provide protection of the environmentfrom the release of radioactive material such as radioactive isotopes,nuclear waste materials, etc., which are chemically bound andencapsulated or entrapped therein. Such glass or silica gel compositionsare characterized by at least 75 mol percent of SiO₂ and by a radiationactivity illustratively above one millicurie, preferably greater thanone curie, per cubic centimeter of said compositions. When highly diluteradwastes are treated with the porous silicate glass or silica gelpursuant to this invention for the purpose of concentrating andimmobilizing the radwaste for storage, the radiation activity of theporous silicate glass or silica gel may not reach the level of onemillicurie per cubic centimeter of the porous silicate glass or silicagel and may remain below 1 microcurie per cc., when it becomes expedientfor other reasons to store, or package in suitable containers, ordispose of as by burial, and/or to collapse the pores of the glass orsilica gel. In concentrating and immobilizing radioactive cations indilute radwastes, the porous silicate glass or silica gel can be loadedup to 10 microcuries per cc. or more but usually is loaded up to 1microcurie per cc. of said porous glass of silica gel. The radioactivematerial is in the form of radioactive cations that are bonded tosilicon by divalent oxy groups. In one aspect, the amount of radioactivematerial contained in the novel glass compositions is at least 1 ppb(part per billion based on weight), generally in the form ofsilicon-bonded oxy groups. In the practice of the novel methods wherebyliquid radwaste is "decontaminated", a plurality, e.g., at least fiveand preferably at least ten, of the radioactive species listedhereinafter become bonded to the silicon of the glass through divalentoxy groups. Preferably the novel compositions should contain at least 82mol percent SiO₂, most preferably greater than 89 mol percent SiO₂.

From a practical standpoint, the upper limit of radioactive materialcontained in the silicate glass or silica gel composition will begoverned, to a degree, by such factors as: The SiO₂ concentration in thecomposition, by the concentration and type of other ingredients whichmay be present in the composition such as B₂ O₃, Al₂ O₃, TiO₂, P₂ O₅zirconia, alkali metal oxides and GeO₂, by the type of radioactivematerial, by the volume fraction of the porous structure in the porousglass or silica gel precursor, by the various techniques employed to fixand/or encapsulate the radioactive material in the composition and otherfactors. A typical range of radioactive cation content is about 1 ppb toabout 20,000 ppm, preferably about 10 ppb about 1000 ppm, in the porousglass.

Radioactive materials which can be chemically bound or fixed in theglass or silica gel matrix include radioactive elements (naturallyoccurring isotopes and man-made isotopes and existing as liquids orsolids dissolved or dispersed in liquids or gases), in the form of thecation, such as rubidium, strontium, the lanthanides, e.g., La, Ce, Pr,Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, cobalt, cadmium, silver,zirconium, molybdenum, technetium, niobium, ruthenium, rhodium,palladium, tellurium, cesium, barium, francium, yttrium, radium andactinides, e.g., Ac, Th, Pa, u, Np, Pu, Am, Cm, Bk, Cf, Es, cations.Especially suitable in the practice of the invention are radioactivewastes from nuclear reactors, spent resactor fuel reprocessing, spentfuel storage pools or other radioactive waste producing processes.

In one aspect the silicate glass or silica gel, containing theradioactive cations bonded to silicon through oxy groups pursuant tothis invention, can be further contained within a collapsed glassarticle of a variety of shapes or forms, e.g., glass tube, havingenhanced containment properties and characterized by an outer clad whosecomposition is at least about 90 mol percent silica, preferably greaterthan about 95 mol percent, and whose inner core contains the radioactivematerials. The high silica content of the clad imparts to the articles aconsiderably greater chemical durability and resistance to leaching byground waters. The inner core has a lower silica concentration of theorder of at least about 70 mol percent silica, preferably about 82 molpercent, and most preferably about 89 mol percent.

In one aspect, the broad invention is directed to novel methods whichinvolve ion-exchanging non-radioactive cations (alkali metal, Group Ib,and ammonium cations) bonded to silicon through divalent oxy groups in aporous silicate glass (which is preferred) or silica gel matrix viaimpregnation techniques which desirably involve impregnation with aliquid and desirably still with an aqueous medium, of pH varying from 2to 13, suitably from about 4 to 11, preferably from about 6 to about 9.5for various preferred embodiments. The impregnating medium containsradioactive species including radioactive cations and the cationexchange reaction occurs on the surfaces of said glass or gel, inparticular, on the surfaces of the myriad of interconnecting porousstructure thereof. Thus, the non-radioactive metal or ammonium cationsare displaceable by said radioactive cations thereby resulting in anexchange of the radioactive cations for said non-radioactive cationswhereby the radioactive cations are chemically bonded to silicon throughthe divalent oxygen linkages. Thereafter, the resulting porous silicateglass or silica gel can be stored, or packaged or "containerized" insuitable containers or forms, or disposed of as by underground burial orby burial at sea, and/or the pores thereof can be collapsed by heatingthereby fixing and/or mechanical encapsulating the radioactive cationswithin a resultant chemically inert, non-porous glass product.

When heating to collapse the pores, the impregnated porous glass orsilica gel can be dried to remove liquid, such as any solvents and/orvolatile materials in the pores and/or it can be washed to remove anysolvents or unreacted materials residing within the pores or on thesurface of the glass or silica gel followed by drying to remove thewashing solvent.

Various aspects of the invention are directed to novel methods for"decontaminating" radioactive waste streams which contain cationicradioactive species therein, especially radioactive streams such as theradioactive primary coolant water of the boiling water reactor system,the radioactive secondary coolant water (which drives the turbine) inthe pressurized water reactor system, and generally the liquid radwastesexemplified previously which accumulate during the operation of suchsystems, by impregnating the porous glass or silica gel discussed hereinwith such streams thus chemically binding radioactive cationic speciesthrough divalent oxy groups to the Si of the glass or gel. The preferredmethods contemplated by the practice of the invention utilize thesilicate glass discussed herein rather than the silica gel since muchlesser amounts of silica are dissolved into the system. This is ofespecial importance since the (primary and secondary) coolant waters arecontained in a closed circulating system and a build up of silica inthese coolant waters is not desirable. When liquid radwaste is disposedof as in a river, the silica build up does not appear to be a problem.

Particularly desirable embodiments of the invention are directed tonovel methods which utilize porous silicate glass (preferred)characterized by ammonium cations (preferred) bonded through divalentoxy groups to silicon to remove radioactive cationic species and othercationic species from the primary coolant water of a (BWR) boiling waterreactor system and/or the secondary coolant water of a (PWR) pressurizedwater reactor system, the pH being maintained in the range ofapproximately neutral to low-medium basicity, preferably from about 7 toabout 9.5, and preferably still from above about 7 to about 9. Poroussilicate glass (preferred) having hydroxyl groups bonded to silicon canbe used as the ion-exchanger per se in the aforesaid (BWR) primarycoolant water, the pH range thereof then being adjusted by the addition,desirably intermittent addition, of ammonium hydroxide thereof. In thismanner the proton (H⁺) of the hydroxyl group is exchanged with cationicammonium. Since the ammonium species when subjected to relatively highradiation can convert to acids or acidic species, e.g., nitrates,continuous monitoring and adjustment of the pH range are precautions tofollow. In these particular embodiments the porous silicate glasscontaining bonded cationic ammonium can suitably replace, in total or inpart, the so-called conventional and literature described condensatepolishers, e.g., deep bed type which generally consists of standarddemineralizer vessels filled with a neutral form of mixed-bed ionexchange resins and/or filter/demin type which is essentially a largeprecoated filter that utilizes a powdered HOH form of ion exchangemedium instead of the standard diatomatious earth.

Still further desirable embodiments of the invention are directed tonovel methods which utilize porous silicate glass (preferred)characterized by lithium cations (preferred) bonded through divalent oxygroups to silicon to remove radioactive cationic species and othercationic species from the primary coolant water of a (PWR) pressurizedwater reactor system, the pH range of this system being maintained fromapproximately 6 to 8, suitably from about 6 to approximately 7. Atypical PWR water chemistry includes:

    ______________________________________                                        Boron                up to 4000 ppm*                                          Lithium as .sup.7 Li, ppm                                                                          0.2 to 6 ppm                                             Total silica as SiO.sub.2                                                                          200 ppb** (max)                                          Chlorides as Cl.sup.-                                                                              0.2 ppm (max)                                            Hydrogen as H.sub.2, Std                                                                           20-40                                                    cc/Kg H.sub.2 O                                                               Total Dissolved Gases,                                                                             100                                                      Std cc/Kg H.sub.2 O                                                           Total suspended solids                                                                             1 ppm (max)                                              ______________________________________                                         *ppm = parts per million                                                      **ppb = parts per billion                                                

In these latter embodiments the lithium bonded ion-exchange glass ismulti-functional inasmuch as it can function as a cationic exchanger, asa corrosion inhibitor by "adjusting" the pH (due to the large quantitiesof the chemical shim, boron, in the PWR coolant) to a weakly acidic pHrange, and as a filter medium. As such, well known and described mixedbed ion exchangers and/or filters (as in condensate polishers) of a PWRsystem can be replaced in part or in toto by the lithium bonded poroussilicate glass (preferred).

Advantages to be noted at this time is the fact that conventionalorganic ion-exchange resins used in PWR and BWR systems to"decontaminate" coolant water and radwaste streams decompose or losestheir stability during operation especially when the resin acquires oris exposed to radiation of certain levels of intensity, e.g., 10⁸ rad.Such decomposition or loss of stability is not manifest in theutilization of the cation exchange porous silicate glass or silica geldescribed herein. Additionally, it has been observed that one unitvolume of said glass or gel can "concentrate" the radioactive cationicspecies contained in upwards of ten unit volumes of BWR coolant and/orPWR coolant and/or liquid radwaste as compared with molecular stuffingtechniques wherein maximum concentration is manifest by merelyintroducing and causing precipitation of cationic species from two orperhaps three unit volumes of simulated coolants of liquid radwaste perunit volume of said glass or gel. Also, the cation exchange porous glassin particulate form, e.g., bead, packing, etc., convenientlycontainerized, for example, in a column is highly efficient inasmuch asit allows much greater throughputs of PWR coolant, BWR coolant, and/orliquid radwaste contacting greater surface areas of glass than is thecase when utilizing comparable dimensioned organic cationic exchangecolumn.

The porous silicate glass or silica gel is made in such manner as tocontain non-radioactive cations selected from the group consisting ofalkali metal cations, Group Ib metal cations and/or ammonium cationsbonded to silicon through divalent oxy linkages --O--. Silicate glass asformed by the phase-separation and acid leaching process contains largeamounts of silicon-bonded hydroxyl groups. We have found that theprotons of these silicon-bonded hydroxyl groups exchange readily withother cations only under highly alkaline conditions. Because of this, itis difficult or impractical to utilize such glasses to process mosttypes of radioactive wastes especially those of the type that decompose,precipitate or are otherwise adversely affected by alkaline agents.

Furthermore, in most cases, radiactive wastes, such as those resultingfrom reactor-fuel reprocessing are highly dilute aqueous solutions. Theadjustment of such solutions to a high enough pH to provide effectiveion exchange with protons of silicon-bonded hydroxyl groups of the glassrequires the addition of large amounts of an alkaline substance and, inthose cases where the reclaimed water to be recycled back to thereprocessor or the reactor is being treated, the pH needs to besubsequently compensated which requires the addition of large amounts ofacidic materials. Thus, ion exchange treatment techniques utilizingporous silicate glass or silica gel containing silicon-bonded hydroxylgroups is at best uneconomical and impractical. In contrast, it has beenunexpectedly found that, when the protons of the silicon-bonded hydroxylgroups are replaced with alkali metal cations (preferred) and/or GroupIb cations and/or ammonium cations (preferred) the radioactive cationsreadily exchange with such monovalent cations at acid, neutral oralkaline pH, thus, making it unnecessary to adjust the pH of theradioactive material being impregnated into the pores of the poroussilicate glass or silica gel.

It has also been unexpectedly found that radioactive cations can besubstantially completely removed from very dilute solutions ordispersions thereof in water. For example, water containing radioactivecations can be purified down to a few parts per billion of radiactivecations by treatment with porous silicate glass or silica gel having theabove-described monovalent cations bonded to silicon through divalentoxygen linkages. It has also been unexpectedly found that theimpregnation of the porous silicate glass or silica gel requires arelatively short period of time for effecting reasonably extensive ionexchange.

In the embodiment where an outer clad containing essentially noradioactive material is disposed around a core containing theradioactive material, the porous silicate glass or silica gel can beplaced within a non-porous tube of Vycor glass or other appropriateglass and then is impregnated with the radioactive material.Subsequently, during or after heating to collapse the pores of thesilicate glass or silica gel the tube is caused to collapse the tubearound the silicate glass or silica gel. A vacuum can be created withinthe tube to facilitate the collapsing of the tube on the silicate glassor silica gel.

The literature adequately describes the preparation of the poroussilicate glass compositions. Suitable glass compositions which may beutilized in the novel methods generally contain SiO₂ as a majorcomponent, have a large surface area and have large amounts ofsilicon-bonded hydroxyl groups on their surfaces. In the practice ofvarious embodiments of the invention the SiO₂ content of the porousglass or silica gel desirably is at least about 75 mol percent SiO₂,preferably at least about 82 mol percent SiO₂, and most preferably atleast about 89 mol percent SiO₂. Such glasses are described in theliterature, see U.S. Pat. Nos. 2,106,744; 2,215,036; 2,221,709;2,272,342; 2,326,059; 2,336,227; 2,340,013; 4,110,093 and 4,110,096, forexample. The disclosures of the last two mentioned patents areincorporated herein by reference.

The porous silicate glass compositions can also be prepared in themanner described in U.S. Pat. No. 3,147,225 by forming silicate glassfrit particles, dropping them through a radiant heating zone whereinthey become fluid while free falling and assume a generally sphericalshape due to surface tension forces and thereafter cooling them toretain their glassy nature and spherical shape.

In general, the porous silicate glass can be made by melting analkali-borosilicate glass, phase-separating it into two interconnectedglass phases and leaching one of the phases, i.e., the boron oxide andalkali metal oxide phase, to leave behind a porous skeleton comprisedmainly of the remaining high silicate glass phase. The principalproperty of the porous glass is that when formed it contains a largeinner surface area covered by silicon-bonded hydroxyl groups. We preferto use porous glass made by phase-separation and leaching because it canbe made with a high surface area per unit volume and has small poresizes to give a high concentration of silicon-bonded hydroxyl surfacegroups, and because the process of leaching to form the pores leavesresidues of hydrolyzed silica groups in the pores thus increasing thenumber of silicon-bonded hydroxyl surface groups present. The poroussilicate glass may be in the shape of a suitable geometric ornon-geometric container such as a cylinder, or it may be in particulateform such as powder, beads, spheroid, etc., desirably contained in asuitable container or conforming to the shape of the container such as acolumn, nylon bag, cube, plate-like membrane, cylinder, sphere, etc.,and thereafter (or prior thereto) ion-exchanged so that the protons ofthe silicon-bonded hydroxyl groups are replaced with alkali metalcations and/or Group Ib cations and/or ammonium cations.

The literature also adequately describes the preparation of silica gelcompositions which can be employed in this invention. These materialsare available, for example, as LUDOX silica gel sold by E. I. DuPont deNemours & Co. which contains 0.08 to 0.6 wt. percent Na₂ O as titratablealkali believed to be present as silicon-bonded NaO-groups.

The porous silicate glass or silica gel contains about 0.3 mol percentto about 10 mol percent, preferably about 1 mol percent to about 10 molpercent, most preferably about 3 mol percent to about 5 mol percent, ofnon-radioactive metal or ammonium cation oxy groups, i.e., alkali metal,Group Ib metal and/or ammonium cation oxy groups. The surface to weightratios for the porous silicate glass and/or silica gel employed in ourinvention are at least about 0.1 m² /g to at least several thousand m²/g, e.g., 10,000 m² /g. preferably at least upwards of 100 m² /g.Desirably, the surface to weight ratio of the starting silicate glass orsilica gel ranges from about 5 to about 1500 m² /g. In the case of theporous silicate glasses used herein, the protons of the silicon-bondedhydroxyl groups are ion exchanged for the alkali metal, Group Ib metaland/or ammonium cation, e.g., sodium hydroxide, potassium hydroxide,cesium hydroxide, lithium hydroxide, rubidum hydroxide, cuprichydroxide, cuprous hydroxide, ammonium hydroxide and such salts of thesemetals, that are capable of exchanging the salt cations for the protonsof the silicon-bonded hydroxyl groups, such as their nitrates, sulfate,acetates, bromides, phosphates, chlorides and the like of these metalsincluding silver nitrate, gold nitrate, sodium nitrate, cesium nitrate,lithium nitrate, cupric nitrate and the like. As indicated hereinabove,suitable non-radioactive metal cations for exchange with the protons ofsilicon-bonded hydroxyl groups, i.e., for attachment to silicon throughdivalent oxygen and subsequent displacement by the radioactive cation,include sodium, potassium, cesium, rubidium, lithium, copper (cupricand/or cuprous), silver, gold and ammonium.

The proportion or concentration of silicon-bonded hydroxyl groups on theporous silicate glass surfaces can be regulated by regulating thesurface area of the porous silicate glass during its preparation as iswell-known in the art. Generally, the surface area is controlled by thetemperature and time at temperature during the phase-separation portionof the preparation of the porous silicate glass. Thus, the longer thetime at temperature and/or the higher the temperature used in thephase-separation, the greater the pore diameter and, therefore, thesmaller the surface area per gram in the resulting porous silicateglass. Conversely, the surface area, and thus the proportion of surface.tbd.SiOH groups available for ion exchange with alkali metal, Group Ibmetal and/or ammonium cations, can be increased by lowering the timeand/or temperature of the heat treatment used to inducephase-separation.

The silicon content of the borate rich phase formed in the manufactureof porous glass precipitates as silica gel during the leaching of theporous glass and this precipitate greatly increases the surface area andthe proportion of silicon-bonded hydroxyl groups available for ionexchange with the alkali metal, Group Ib metal and ammonium cations.Thus, an additional technique for increasing the surface area and theproportion of silicon-bonded hydroxyl groups is to start with acomposition which will produce large quantities of a silica gelprecipitate. This can be accomplished by increasing the amount of silicainitially used in the composition from which the glass is made. Anyother techniques known by the skilled worker for increasing, ordecreasing if desired, the proportion of surface .tbd.SiOH groups can beused to provide a porous glass having the desired proportion of surfacesilicon-bonded hydroxyl protons available for exchange by alkali metal,Group Ib metal and/or ammonium cations.

It is preferred to react the porous silicate glass containingsilicon-bonded hydroxyl groups with the appropriate salt of thenon-radioactive alkali metal, Group Ib and/or ammonium cation at asufficiently high pH to bring about the exchange of the metal orammonium cation of the salt with the proton of the silicon-bondedhydroxyl groups but not so high that substantial amounts of the glassdissolves or begins to dissolve. There is a loss of surface areaassociated with this dissolution of the porous glass at excessively highpH's and thus a loss of silicon-bonded hydroxyl groups and/orsilicon-bonded non-radioactive metal or ammonium cation oxy groups. Apreferred method of exchanging the protons of silicon-bonded hydroxylgroups is to treat the porous silicate glass with a salt of the alkalimetal, and/or Group Ib metal buffered with ammonium hydroxide orotherwise buffered at a pH of about 11 to about 13. It has been foundthat the buffering with ammonium hydroxide of the primary ion exchangeof said non-radioactive metals for the protons of the silicon-bondedhydroxy groups in this manner avoids significant loss of glass orsurface area.

The proportion of silicon-bonded alkali metal oxy, Group Ib metal oxyand/or ammonium oxy groups can be regulated by several techniques. Ofcourse, the proportion of silicon-bonded hydroxyl groups in the porousglass will determine generally the maximum amount of silicon-bondedmetal or ammonium oxy groups obtainable. Longer times of contact of thealkali metal, Group Ib metal and/or ammonium hydroxides and/or saltswith the porous glass will increase the proportion of silicon-bondedmetal or ammonium oxy groups. Also, the smaller the particle size of theporous glass, the greater the proportion of silicon-bonded metal oxy orammonium oxy groups within a given time. Any other suitable techniquecan be used to regulate the proportion of silicon-bonded metal oxy orammonium oxy groups to the desired level.

As mentioned above, silica gel containing silicon-bonded non-radioactivemetal cation, and/or ammonium cation, oxy groups are availablecommercially. They can also be obtained by precipitating the silica gelfrom an aqueous solution of the silicate of the non-radioactive cationsuch as sodium silicate, potassium silicate, lithium silicate and thelike using an appropriate acid, such as hydrochloric acid, nitric acidor the like. The concentration of the silicon-bonded non-radioactivemetal cation oxy groups, e.g., silicon-bonded sodium oxy groups in thesilica gel can be regulated by regulating the amount of acid used. Whenlarger amounts of acid are used, lower concentrations of thenon-radioactive metal cation oxy groups result. The surface area can beregulated by the reaction conditions employed and these techniques arewell known in the prior art. The concentration of the silicon-bondednon-radioactive metal cation oxy or ammonium oxy groups can be increasedby treating the silica gel with additional solution of thenon-radioactive metal cation or ammonium cation as described hereinabovefor the porous silicate glass or, preferably the silica gel can betreated with an appropriate non-radioactive metal cation or ammoniumcation salt buffered with ammonium hydroxide also as hereinabovedescribed in relation to the porous silicate glass. Furthermore, thetype of non-radioactive metal or ammonium cations bonded to siliconthrough oxy groups can be changed, e.g., NaO groups can be changed toother silicon-bonded non-radioactive metal oxy groups by reacting withthe desired non-radioactive metal cation or ammonium salt.

When lithium is employed as the non-radioactive metal cation bonded tosilicon through divalent oxygen linkage in the porous silicate glass orsilica gel employed in this invention, the presence of large amounts oflithium in the final sintered, fused or collapsed silicate glass orsilical gel composition can cause crystallization therein.Notwithstanding such crystal formation, the radioactive cations arechemically bonded to silicon through divalent oxy groups and in suchform remain "tied" to the final sintered, fused or collapsedcomposition.

The porous glass preforms, such as the small, short rods or small sphereor powders, or other particulate form, can be employed to removeradioactive cations from highly dilute solutions of same. For example,solutions containing as little as 1 ppt (part per trillion) based onweight, i.e., 1 wt. part per 10¹² wt. parts solution of radioactivecations can be purified by contacting such solutions with the porousglass preforms or the silica gel in the manner described hereinabove.This contact can take place in an ion exchange column packed with theporous silicate glass or silica gel preforms and the radioactivecation-containing waste solution can then be passed down through thecolumn to remove the radioactive cation content of the solution.Alternatively, the porous glass preforms or silica gel can be added tothe radioactive cation-containing solution and stirred therein for aperiod of time that permits the maximum exchange of the radioactivecation for the silicon-bonded non-radioactive cation. Dilute solutionshaving less than 0.01 microcurie radioactivity per ml as well as moreconcentrated solutions, e.g., those having 1 curie or more radioactivityper ml and those solutions between 0.01 microcurie and 1 curieradioactivity per ml are efficiently treated by this invention.

In a typical nuclear reactor there are several sources of radwaste asdescribed hereinabove that must be safely contained. These includehighly dilute liquid waste streams which can contain dispersedradioactive solids as well as dissolved radioactive cations;concentrated liquid wastes which can contain radioactive cations,radioactive anions and radioactive solids (such wastes are the result ofthe boiling down of primary coolant containing boric acid as a chemicalshim and the boiling down of used regeneration solutions from theregular ion exchange beds customarily used); and/or radioactive gasessuch as radioactive krypton and/or radioactive iodine. Therefore, oneuse of our invention is in the provision of a total radwaste disposalsystem wherein the porous glass or silica gel of this invention havingsilicon-bonded alkali metal oxy, Group Ib metal oxy, and/or ammonium oxygroups is packed into an cation exchange column which preferably is afusible glass column. It is preferred that the porous glass or silicagel be finely divided and sieved to a suitable size to maximize the rateof flow of the radwaste stream through and between the particles of theporous glass or silica gel and to also minimize the ion exchange time.First, the dilute radwaste stream is passed through the column and theradioactive cations in solution are cation exchanged with the alkalimetal, Group Ib metal and/or ammonium cations in the porous glass orsilica gel to chemically bond the radioactive cations to the glass orsilica gel. If the dilute radwaste stream is to be reused as the primarycoolant, it is conventional to add lithium ions as a corrosioninhibitor. Therefore, it can be advantageous to utilize a porous glassor silica gel having silicon-bonded lithium oxy groups so that lithiumions (which do not become radioactive as do sodium ions) are released tothe coolant stream as radioactive cations are removed from it.Additionally, dispersed radioactive solids in the dilute radwaste streamcan be mechanically filtered on the porous glass or silica gel particlesin the column as the stream percolates through and between theparticles. In order to maintain the ratios of solids in the radwastestream to the porous glass or silica gel small enough to maintain thefiltering action as the solids accumulate on the porous glass or silicagel particles, fresh porous glass or silica gel particles can be addedto the column.

After the column has been exhausted of its ion exchange capacity by thedilute liquid radwaste stream, it can be dried and the concentratedliquid radwaste (containing concentrated boric acid, for example, at atemperature of 100° C.) can be added to the column. Thus, the pores ofthe porous glass or silica gel can be stuffed with the radioactivesolids, cations and anions contained by the concentrated radwaste.Excess boric acid then can be washed from between the particles of theporous glass or silica gel using cold water (less than 30° C.) and theparticles can be dried to deposit the radioactive solids, cations andanions within the pores of the porous glass or silica gel usingtechniques taught in U.S. Pat. No. 4,110,096. Thereafter, the column canbe evacuated and the radioactive gases can be introduced into the glasscolumn, then the column can be heated to collapse the pores of theporous glass or silica gel and to collapse the glass column therebyimmobilizing and containing the exchanged radioactive cations, theradioactive solids on the exterior of the porous glass or silica gelparticles, the radioactive solids, anions and/or cations deposited inthe pores of the porous glass or silica gel and the radioactive gascontained by the glass column. Suitable pressure differentials can beused to facilitate the collapsing of the glass column. Heating can becontinued to cause the porous glass or silica gel particles to stick toeach other to further trap interstitial radioactive solids between theparticles. Upon cooling there results a highly durable solid whicheffectively contains the radioactive waste introduced into the glasscolumn.

Some of the nuclear reactor streams may be basic because some elementsin the radwaste appear as anions, e.g., chromium, molybdenum,praseodymium and cerium anions, which, of course, have to be immobilizedalso. One way to accomplish this is to pass the basic radwaste streamthrough a customary anion exchange resin column. The column isregenerated with non-radioactive base, e.g., ammonium hydroxide. Theeffluent from said regeneration contains a higher concentration ofradioactive (pernicious) elements and is boiled down in a boiler toprovide a reduced volume of basic radwaste. When the concentrated basicradwaste in the bottom of the boiler is acidified under reducingconditions, some of the anions, e.g., Cr, Mo, Ce and Pr become cationswhich can be ion-exchanged with and removed by the above-mentionedporous glass columns. The boiler bottoms are defined as the concentratedsolution or raffinate which remains after boiling down the solution andit may contain solids. It can be molecularly stuffed into the porousglass to become a highly durable solid waste product.

There are many other industrial wastes which have to be eliminated fromwaste streams which, although not radioactive, are very poisonous tohumans. For example, it has been well publicized that water bodies havebeen contaminated in the past with mercury, cadmium, thallium, lead andother heavy metal cations. Often the concentration of such cations inthe waste streams is very low, thus presenting the problem of treatinglarge volumes of water containing small amounts of toxic cations.Nevertheless, overall, large quantities of such contaminants do enterthe ecosphere. The present invention can purify such waste streams byion-exchanging into the porous glass or silica gel the poisonous cationswhich can later be immobilized by heating the glass to collapse thepores.

This invention can be employed for concentrating and immobilizingradioactive cations in a glass or silica gel for extremely long timestorage. When applicable, silicate glass or silica gel loaded withradioactive cations bonded to silicon through divalent oxygen linkagescan be appropriately package in containers, e.g., steel, concrete,urea-formaldehyde formulations, etc., and buried beneath the earth'esurface or dumped into the ocean. Alternatively, the radioactivity ofthe sintered glass or silica gel containing the silicon-bondedradioactive cation oxy groups can be utilized in suitable devices orinstruments for a variety of purposes, such as, destroyingmicroorganisms, e.g., in the preservation of food, or in sterilizingsewage sludge or for any other purpose where radioactivity can beemployed constructively.

The following examples are presented. Unless otherwise specified allsolutions are aqueous solutions, the "aqueous ammonium hydroxide" or"NH₄ OH" used in the Examples contains about 28% NH₃, ppm means partsper million parts of solution, ppb means parts per billion parts ofsolution, ppt means parts per trillion parts of solution, all parts andpercentages are on a weight basis and all temperatures are given indegrees Centigrade.

EXAMPLE 1

This example illustrates the preparation of the porous glass that isused in the subsequent examples.

In the subsequent examples, unless otherwise specified, the porous glassthat is used is in the form of cylinders 6 to 9 mm in diameter and oneto several centimeters in length. The porous glass is formed by themethod disclosed hereinabove; that is, a mixture of powders of silica,boric acid, sodium carbonate and potassium carbonate is prepared in suchproportions that yield a glass nominally comprising 3.5 mol percent Na₂O, 3.5 mol percent K₂ O, 33 mol percent B₂ O₃ and 60 mol percent SiO₂.The mixture is heated in a Pt crucible up to 1400° C. in an electricfurnace and thus is melted into a molten glass which is pulled into rodsabout 8 mm in diameter and cut to about 2.5 cm long. After cooling, theglass is phase-separated by heat treating at 550° C. for 2 hours andthen is leached in a 3N HCl bath at 95° C. for three days.Phase-separation results in two phases; one, a high silica phase and alow silica phase comprising the remaining silica, boron trioxide andalkali metal oxide. Leaching removes the boron-rich phase leaving behinda porous glass comprising about 95 mol percent SiO₂ and about 5 molpercent B₂ O₃ and having interconnected pores and at least about 5.6 molpercent silicon bonded hydroxyl groups.

Subsequent rinsing in water yields a porous glass preform ready for usein the following examples.

EXAMPLES 2-10

In these examples, the porous glass rods prepared in the mannerdescribed in Example 1 are subjected to primary ion exchange byimmersing them in the primary solutions, correspondingly described inTable 1 below for each of Examples 2-10, for about two to three days atabout 20° C. The resulting impregnated rods are then rinsed in deionizedwater until the rinse water has a pH of about 8. The rinsing step isconducted to remove unreacted primary cations in the pores of the glassand leave only those which are chemically bonded to the glass throughsilicon-bonded oxygen. The rods are cut in half. One half of the rodsare analyzed for the concentrations of the primary cations in the glassrods and said primary ions and concentrations are correspondingly listedin Table 1.

                  TABLE 1                                                         ______________________________________                                        Primary Ion-Exchange                                                          Ex-  Pri-                        Concentration of pri-                        am-  mary    Primary             mary cation in glass as                      ple  Cations Solution     pH     weight percent oxide                         ______________________________________                                        2    Na      25 g NaNO.sub.3 +                                                                          12.4   1.2  (Na.sub.2 O)                                         50 ml NH.sub.4 OH                                                3    "       25 g NaNO.sub.3 +                                                                          "      1.2  "                                                    50 ml NH.sub.4 OH                                                4    "       25 g NaNO.sub.3 +                                                                          "      1.2  "                                                    50 ml NH.sub.4 OH                                                5    "       30 g NaNO.sub.3 +                                                                          "      2.0  "                                                    100 ml NH.sub.4 OH                                               6    "       30 g NaNO.sub.3 +                                                                          "      2.0  "                                                    100 ml NH.sub.4 OH                                               7    "       30 g NaNO.sub.3 +                                                                          "      2.0  "                                                    100 ml NH.sub.4 OH                                               8    "       30 g NaNO.sub.3 +                                                                          "      2.0  "                                                    100 ml NH.sub.4 OH                                               9    K       6 g KNO.sub.3 +                                                                            12.1   4.24 (K.sub.2 O)                                          24 ml NH.sub.4 OH +                                                           74 ml H.sub.2 O                                                  10   Cs      12 g CsNO.sub.3 +                                                                          "      11.97                                                                              (Cs.sub.2 O)                                         74 ml H.sub.2 O +                                                             24 ml NH.sub.4 OH                                                ______________________________________                                    

The NH₄ OH used in Examples 2-10 is a 16 Molar solution.

The glass rods in Examples 2-4 contained 2.4 mol percent Na cations,those of Example 5-8 contained 4 mol percent Na cations, that of Example9 contained 5.5 mol percent K cations and that of Example 10 contained5.6 mol percent Cs cations wherein said cations are bonded to siliconthrough an oxy linkage. A significant yet unmeasured amount of NH₄ ⁺bonded to silicon through oxy linkages in the glass also results. Theirpresence is demonstrated in Examples 22 and 23. The mole percents of themetal cations were calculated by multiplying the mole percent of thecorresponding metal oxides by the number of cations per molecule.

The other half of the rods is immersed in a secondary solutioncontaining different cations for the secondary ion exchange. Thesecondary ions are listed and the secondary solutions are described inTable 2. Soaking in these secondary solutions is at room temperature forfour days.

After soaking in the secondary solutions, the rods are then washed withdeionized water for a minimum of three days until the pH of the washwater decreases to about 8. The washing step is conducted to removeunreacted secondary cations in the pores of the glass and leave onlythose which are chemically bonded to the glass through silicon-bondedoxygen.

The rods are dried in a desiccator at 20° C. for two days and then invacuo overnight at 0° C. They are subsequently transferred to a furnaceand heated to between 860° and 890° C. whereby sintering of the poresoccurs yielding solid rods containing the secondary cations chemicallybound as an integral part of the structure of the glass.

The rods are then dissolved in hydrofluoric acid and the resultingsolutions are analyzed by atomic absorption for the amount of each ofthe primary and secondary cations chemically bound to the glass prior todissolution in hydrofluoric acid. The results of these analyses aregiven in Table 2 below.

                                      TABLE 2                                     __________________________________________________________________________    Secondary                                                                     Ion Exchange               Analysis of Final Product                               Secondary                                                                           Secondary       Conc. of primary cations                                                                  Conc. of secondary cations             Example                                                                            Cation                                                                              Solution      pH                                                                              as wt % oxide (1)                                                                         as wt % oxide (2)                      __________________________________________________________________________    2    Cs    5 g CsNO +    5.6                                                                             0.2   (0.4) 5.3 (Cs.sub.2 O)                                                                       (2.4)                                    50 ml H.sub.2 O                                                    3    Nd    50 g Nd(NO.sub.3).sub.3.5H.sub.2 O +                                                        1.4                                                                             0.3   (0.6) 0.7 (Nd.sub.2 O)                                                                       (0.26)                                   33 ml H.sub.2 O                                                    4    Fe    30 g Fe(NO.sub.3).sub.3.9H.sub.2 O +                                                        0.7                                                                             0.04  (0.08)                                                                              0.4 (Fe.sub.2 O.sub.3)                                                                 (0.3)                                    100 ml H.sub.2 O                                                   5    Sr    98 ml H.sub.2 O + 5 g H.sub.3 BO.sub.3 +                                                    3.7                                                                             0.2   (0.4) 4.2 (SrO)                                                                              (2.5)                                    16 g Sr(NO.sub.3).sub.2                                            6    Co    91 ml H.sub.2 O + 5 g H.sub.3 BO.sub.3 +                                                    3.8                                                                             0.2   (0.4) 2.7 (CoO)                                                                              (2.2)                                    22 g Co(NO.sub.3).sub.2                                            7    Cs    93 ml H.sub.2 O + 5 g H.sub.3 BO.sub.3 +                                                    4.4                                                                             0.2   (0.4) 9.7 (Cs.sub.2 O)                                                                       (4.4)                                    15 g CsNO.sub.3                                                    8    Fe    87 ml H.sub.2 O + 5 g H.sub.3 BO.sub.3                                                      0.7                                                                             0.04  (0.08)                                                                              0.9 (Fe.sub.2 O.sub.3)                                                                 (0.7)                                    30 g Fe(NO.sub.3).sub.3.9H.sub.2 O                                 9    Cu    11.2 g Cu(NO.sub.3).sub.2.98                                                                4.5                                                                             0.32  (0.4) 5.3 (CuO)                                                                              (4.1)                                    ml H.sub.2 O                                                       10   Na    5.1 g NaNO.sub.3                                                                            5.7                                                                             5.99  (2.6) 0.96                                                                              (Na.sub.2 O)                                                                       (2.0)                                    100 ml H.sub.2 O                                                   __________________________________________________________________________     (1) Mol % of primary cations bonded to silicon by oxy linkages are given      in the parentheses.                                                           (2) Mol % of secondary cations bonded to silicon by oxy linkages are give     in the parentheses.                                                      

It is noted that the secondary solutions that are used for the secondarycation exchange are on the whole neutral or mildly acidic. As pointedout hereinabove, except for very strongly acid solutions where the pH isbelow about 2 as in Examples 3, 4 and 8 where less of the secondarycations was retained by the porous glass through ion exchange, there areno restrictions on the types of solutions which may be used in thesecondary cation exchange part of the process.

It is also noted from the cesium and iron examples in Tables 1 and 2that the concentration of the secondary cations which are picked upduring the secondary cation exchange part of the process is stronglydependent on the initial concentration of the primary cations that areused for the preceding primary cation exchange.

EXAMPLES 11-19

The procedures described for Examples 2 through 10 are respectivelycarried out in Examples 11 through 19 except that the secondary cationsand secondary solutions are radioactive; otherwise all steps,proportions, materials and conditions are the same. The concentrationsof radioactive cations chemically bound in the final glass product areessentially the same as those concentrations correspondingly given inTable 2 for Examples 2-10.

EXAMPLES 20 AND 21

In Example 20, silica gel purchased from DuPont as Ludox HS-40% ispoured into a Vycor glass* tube plugged with a filter at the bottom toprevent the silica gel particles from escaping. Analysis of the silicagel (Ludox HS-40%) by atomic absorption before starting shows that itcontains 40 wt.% SiO₂, 0.41 wt.% titratable alkali as Na₂ O less than0.1 wt.% Cs₂ O, and a ratio of SiO₂ to Na₂ O of about 95 to 1. Thesilica gel contained about 0.4 mol percent silicon-bonded sodium oxygroups. The titratable sodium content is believed to be in the form ofsilicon-bonded sodium oxy groups and the surface to weight ratio isabout 230 m² /g. An essentially neutral solution containing 10 g CsNO₃per 100 ml of water is passed slowly through the silica gel. Afterseveral liters are passed through, the silica gel is dried and heated invacuum about 100° C. until the silica gel is observed to sinter (below1000° C.) and then it is heated further with a vacuum in the Vycor tubeto collapse the tube on the sintered silica gel (which normally occursbelow 1300° C.). The final product, after cooling to room temperature isa solid rod with the outside surface consisting of at least 94% silica(i.e., the composition of the Vycor tube), and an interior containing Csbonded to silicon through oxygen linkage and fused into the structure.Cesium oxide content is analyzed by atomic absorption spectroscopy to beat or above 2 weight percent based on the weight of silica gel.Sometimes the rods break into several pieces, but this does notsignificantly affect the fixation behavior of the glass.

Example 21 is carried out in exactly the same manner as described abovewith the only exception being that the CsNO₃ is radioactive. Thereresults a final product in which the radioactive Cs is chemically bondedthrough oxy linkages to silicon of the silica gel within the collapsedVycor tube which encapsulates and seals the silica gel from theenvironment.

EXAMPLES 22 AND 23

In each of these examples, porous glass rods measuring 9.3 mm indiameter and 74 mm long are prepared in the manner described in Example5 by a primary ion exchange treatment of porous glass in a 3.2M sodiumnitrate-ammonium hydroxide solution for three days followed by rinsingwell with deionized water until the pH of the rinse water was reduced toabout 8. The rods so treated contained 2.0 wt.% silicon-bonded sodiumoxy groups expressed as Na₂ O, i.e., 4.0 mol percent sodium cationsbonded to silicon through oxy linkages. The wet rods were then immersedin an aqueous solution containing 25 ppm of cesium cation (3.74 mgcesium nitrate per 100 ml H₂ O) in the case of Example 22 and in anaqueous solution containing 10 ppm strontium cation (2.35 mg strontiumnitrate per 100 ml H₂ O) in the case of Example 23. The glass rods wereallowed to remain immersed in the respective solutions at about 25° C.for about three days while being stirred. Samples of each solution werewithdrawn periodically for analysis by atomic absorption. These resultsare given in Table 3 below.

                  TABLE 3                                                         ______________________________________                                        Time   Example 22       Example 23                                            Elapsed                                                                              Cs.sup.+  Na.sup.+   Sr.sup.2+                                                                             Na.sup.+                                  (Hrs.) (ppb) (1) (ppb) (2)  (ppb) (1)                                                                             (ppb) (2)                                 ______________________________________                                         0     23000     0-100      8900    0-100                                     41/4   196       0-300      13.9    0-100                                     71/4   119*      13300      9.6     14300                                     24     61*       26000      --      22700                                     48     10.3*     38500      7.8*    27000                                     ______________________________________                                         *Subject to possible wide experimental error                                  (1) By the furnace technique                                                  (2) By the flame technique.                                              

It is noted that the majority of the cesium and strontium cationsdisappear from the solution before an increase of sodium content in thesolution is observed. This suggests that, in addition to the 4 molpercent sodium cations bonded to the porous glass, ammonium cationsprobably were also bonded to silicon through oxy groups by the primaryion exchange.

The pH of each of the Cs⁺ and Sr²⁺ solutions was initially 5.8 and afterthe elapsed time of about 71 hours, the pH of these solutions was about9.

These results illustrate the effectiveness of porous glass materials inremoving cations from very dilute aqueous solutions. In each case ofExamples 22 and 23, over 99 percent of the Cs⁺ ions and Sr²⁺ ions wereremoved within the very short period of 41/2 hours.

EXAMPLES 24 AND 25

The procedures of Examples 22 and 23 are respectively carried out inExamples 24 and 25 except that the Cs⁺ solution and the Sr²⁺ solutioncontains radioactive Cs⁺ and radioactive Sr²⁺ ions, respectively.Otherwise all steps, proportions and conditions are the same.Essentially the same results as are given in Table 3 are obtained,respectively, for Examples 24 and 25.

EXAMPLES 26 AND 27

The procedures of Examples 24 and 25 are respectively carried out inExamples 26 and 27 except that the porous glass rods are replaced byporous glass beads having an average diameter of about 50 to about 100microns. The beads are prepared by the process described in Example 1except that instead of pulling the molten glass into rods, it isquenched by pouring it into a cooling bath of water so as to form smallfractured glass particles (frit) of varied shapes. The glass particlesor frit are then formed into spheres by passing them through a radiantheating zone or high temperature flame where they soften sufficiently topermit surface tension forces to form them into spheres while they arefreely moving through the air. They are then cooled rapidly to preventdevitrification. There are thus formed beads or spheres averaging about50 to about 100 microns in diameter. These beads or spheres are treatedin the manner described in Example 5 to provide porous silicate glassbeads having sodium oxy groups bonded to silicon on the inner surfacesof the pores thereof.

An ion exchange column is filled with the treated spheres or beads,i.e., the beads having the silicon-bonded sodium oxy groups. Aradioactive waste solution containing radioactive Cs⁺ cations, inExample 26, or containing radioactive Sr²⁺ ions, in Example 27, ispassed through the column. In each case, the aqueous solution comingfrom the bottom of the column is substantially free of radioactivecations.

EXAMPLE 28

This example illustrates a method for treating primary coolant from apressurized water nuclear reactor plant. A mixture of powders of silica,boric acid, sodium carbonate and potassium carbonate is prepared in suchproportions that yield a glass comprising 3.5 mol percent Na₂ O, 3.5 molpercent K₂ O, 33 mol percent B₂ O₃ and 60 mol percent SiO₂. The mixtureis heated in a platinum crucible up to 1400° C. in an electric furnaceto produce a molten glass which is pulled into rods about 8 mm indiameter and about 2.5 cm long. The glass rods are cooled and the glassis phase-separated by heat treating at about 550° C. for about 110minutes. The rods are then crushed to form a powder which is sievedthrough a 32 mesh screen onto a 150 mesh screen. The glass particlescollected on the 150 mesh screen are leached in 3N HCl at about 50° C.for about 6 hours to remove the boron-rich phase and leave behind aporous glass comprising about 95 mol percent SiO₂ and about 5 molpercent B₂ O₃. The porous glass has interconnected pores and contains atleast about 5 mol percent silicon-bonded hydroxyl groups. The glassparticles are then rinsed in deionized water until the rinse waterreaches a pH of about 7.

The porous glass powder is then immersed in an approximate 3.2 molarsodium nitrate-ammonium hydroxide aqueous solution for three days andthen is rinsed in water until the pH of the rinse water is reduced toabout 8. The resulting powder is then placed in an ion exchange columnmade of the Vycor glass as described in Examples 20 and 21. Aradioactive primary coolant from a pressurized water nuclear reactorplant utilizing UO₂ fuel clad in stainless steel (containing 4.9 weightpercent ²³⁵ U) is passed through the column. The primary coolant has thecomposition given in Table 4 below which lists the radionuclide, theprobable source, the probable form and the average concentration inmicrocuries per milliliter. The cationic radionuclides ion-exchange withsodium cations bonded to silicon through oxy groups in the poroussilicate glass powder.

                  TABLE 4                                                         ______________________________________                                                                 Average   Average                                    Radio-                                                                              Probable Probable  Concentration                                                                           Concentration                              nuclide                                                                             Source.sup.a                                                                           Form.sup.b                                                                              (μCi/ml)                                                                             (ppb)                                      ______________________________________                                        3.sub.H                                                                             (1),(2)  Water, gas                                                                              2.4       0.249                                      14.sub.C                 1.2 × 10.sup.-5                                                                   2.69 × 10.sup.-3                     24.sub.Na                                                                           (1)      Cation    1.9 × 10.sup.-2                                                                   2.18 × 10.sup.-6                     32.sub.p                 3.3 × 10.sup.-5                                                                   1.16 × 10.sup.-8                     35.sub.S                   3 × 10.sup.-6                                                                   7.08 × 10.sup.-8                     51.sub.Cr                                                                           (1)      Anion     3.7 × 10.sup.-4                                                                   4.02 × 10.sup.-6                     54.sub.Mn                                                                           (1)      Cation, s 2.7 × 10.sup.-4                                                                   3.38 × 10.sup.-5                     55.sub.Fe                                                                           (1)      Cation, s 1.9 × 10.sup.-4                                                                   7.6  × 10.sup.-5                     59.sub.Fe                                                                           (1)      Cation, s 1.0 × 10.sup.-5                                                                   2.03 × 10.sup.-7                     57.sub.Co                                                                           (1)      Cation, s 1.2 × 10.sup.-6                                                                   1.42 × 10.sup.-7                     58.sub.Co                                                                           (1)      Cation, s 4.7 × 10.sup.- 4                                                                  1.48 × 10.sup.-5                     60.sub.Co                                                                           (1)      Cation, s 7.7 × 10.sup.-5                                                                   6.81 × 10.sup.-5                     63.sub.Ni                                                                           (1)      Cation, s 8.0 × 10.sup.-6                                                                   1.30 × 10.sup.-4                     64.sub.Cu                                                                           (1)      Cation,   5.4 × 10.sup.-4                                                                   1.41 × 10.sup.-7                                    Anion, s                                                       89.sub.Sr                                                                           (2)      Cation    2.8 × 10.sup.-6                                                                   9.93 × 10.sup.-8                     90.sub.Sr                                                                           (2)      Cation      4 × 10.sup.-7                                                                   2.84 × 10.sup.-6                     91.sub.Sr                                                                           (2)      Cation    9.8 × 10.sup.-5                                                                   2.76 × 10.sup.-8                     90.sub.Y                                                                            (2)      s                                                              91.sub.Y                                                                            (2)      s                                                              92.sub.Y                                                                            (2)      s                                                              95.sub.Zr                                                                           (1),(2)  s         1.7 × 10.sup.-5                                                                   8.06 × 10.sup.-7                     95.sub.Nb                                                                           (1),(2)  s         1.9 × 10.sup.-5                                                                   4.83 × 10.sup.-7                     99.sub.Mo                                                                           (1),(2)  Anion     1.2 × 10.sup.-4                                                                   2.54 × 10.sup.-7                     103.sub.Ru                                                                          (2)      s         0                                                    106.sub.Ru                                                                          (2)      s         0                                                    122.sub.Sb                                                                          (1)      s         1.0 × 10.sup.-4                                                                   2.62 × 10.sup.-7                     124.sub.Sb                                                                          (1)      s         2.0 × 10.sup.-5                                                                   1.16 × 10.sup.-6                     132.sub.Te                                                                          (2)      Anion, s                                                       131.sub.I                                                                           (2)      Anion     4.6 × 10.sup.-5                                                                   3.71 × 10.sup.-6                     132.sub.I                                                                           (2)      Anion                                                          133.sub.I                                                                           (2)      Anion     6.2 × 10.sup.-4                                                                   5.5  × 10.sup.-7                     135.sub.I                                                                           (2)      Anion       9 × 10.sup.-4                                                                   2.60 × 10.sup.-7                     134.sub.Cs                                                                          (2)      Cation    4.7 × 10.sup.-7                                                                   3.62 × 10.sup.-7                     136.sub.Cs                                                                          (2)      Cation    0                                                    137.sub.Cs                                                                          (2)      Cation    1.1 × 10.sup.-6                                                                   1.26 × 10.sup.-5                     140.sub.Ba                                                                          (2)      Cation    4.7 × 10.sup.-6                                                                   6.45 × 10.sup.-8                     141.sub.Ce                                                                          (2)      Anion, s  0                                                    143.sub.Ce                                                                          (2)      Anion, s  0                                                    144.sub.Ce                                                                          (2)      Anion, s  0                                                    143.sub.Pr                                                                          (2)      Anion, s                                                       110m.sub.Ag                                                                         (1)      s         1.2 × 10.sup.-5                                                                   2.52 × 10.sup.-6                     181.sub.Hf                                                                          (1)      s           6 × 10.sup.-6                                                                   3.70 × 10.sup.-7                     182.sub.Ta                                                                          (1)      s         2.5 × 10.sup.-5                                                                   4.01 × 10.sup.-6                     183.sub. Ta                                                                         (1)      s         6.2 × 10.sup.-5                                                                   4.34 × 10.sup.-7                     185.sub.W                                                                           (1)      s         1.2 × 10.sup.-5                                                                   1.28 × 10.sup.-6                     187.sub.W                                                                           (1)      s         3.7 × 10.sup.-4                                                                   5.30 × 10.sup.-7                     85m.sub.Kr                                                                          (2)      Gas                                                            85.sub.Kr                                                                           (2)      Gas                                                            88.sub.Kr                                                                           (2)      Gas                                                            133.sub.Xe                                                                          (2)      Gas       8.9 × 10.sup.-5                                                                   4.78 × 10.sup.-8                     135.sub.Xe                                                                          (2)      Gas         9 × 10.sup.-5                                                                   3.54 × 10.sup.-8                     ______________________________________                                         .sup.a (1) Neutron activation products of nuclides from fuel cladding,        constrution material, and water.                                              (2) Leakage from fuel. Mostly fission products.                               .sup.b Gas: presumably as dissolved gas.                                      s: insoluble solids.                                                     

The radioactive cations of the radionuclides listed in Table 4,cation-exchange with sodium cations bonded to silicon through oxy groupsin the porous glass thereby binding the radionuclides to the porousglass through said silicon-bonded oxy groups and releasing sodiumcations to the coolant solution. The insoluble radioactive solids in thecoolant also filter out on the external surfaces of the porous glassparticles. Additional porous glass particles can be added to increasethe filtering capacity of the ion exchange column as the insolublesolids build-up in the column. Under some conditions, mainly dependenton existing governmental regulations, the porous silicate glasscontaining bound cationic radionuclides may be disposed and/or buried orsuitably containerized often times in steel and/or concrete or mixedwith cement powder or urea-formaldehyde formulations and "set" thereinand thereafter disposed and/or buried. The particulate porous glass canbe heated to collapse the pores thereof as described herein.

The anionic radionuclides are not substantially removed in the columnand pass with the coolant through the column. The anionic radionuclidescan be subsequently removed by treatment with conventional anionicexchange resins. Upon regeneration of the conventional anion exchangeresin after it becomes loaded, the regenerant solution containing theanionic radionuclides can be concentrated by evaporation and theresulting concentrate can be molecularly stuffed into the pores of theporous glass in the ion exchange column after said porous glass hadbecome substantially loaded with silicon-bonded radionuclide cation oxygroups. It is preferred to first dry the loaded porous glass so that theanionic radionuclide concentrate can readily enter the pores of theporous glass. The anionic radionuclides can be precipitated or depositedwithin the pores of the porous glass by the careful drying proceduresdisclosed in U.S. Pat. No. 4,110,096. Thereafter, the porous glassparticles can be heated to collapse the pores thereof. Thereafter, ifdesired the column can be heated to collapse the Vycor glass around theparticles thereby enveloping the filtered solids and the glass particlescontaining the cationic and anionic radionuclides within the Vycor glasscolumn. While the glass column cracks because of differential thermalcontraction it still contains and further immobilizes the radioactivematerials and forms a product that is many times more durable thancement or metal drumsheretofore used. There is thus provided a durablepackage of concentrated radionuclides which is highly resistant toleaching by water or other fluids.

As illustrated in Example 28, liquid radwaste that must besatisfactorily treated and disposed of can be highly dilute. The volumeof dilute radwaste treated with a given amount of ion exchange porousglass or silica gel pursuant to this invention can be practicallyunlimited before all the available exchange sites (i.e. silicon-bondedalkali metal oxy, Group Ib metal oxy and/or ammonium oxy groups) in theporous silicate glass or silica gel are filled by radioactive cations.For example, the weight of the dilute liquid radwaste described inExample 28 that could be expected to be treated before exhausting allexchange sites would be of the order of 10⁹ or more times the weight ofthe ion exchange porous glass or silica gel employed. Furthermore, itcould be expected that other parts of the system would require overhaul,e.g., repair or replacement of pumps or piping or other equipment,before the ion exchange silicate glass or silica gel becomes exhausted.Consequently, it is quite possible, if not probable, that theradioactivity of the resulting porous glass or silica gel when disposedof may never reach 1 millicurie or even 1 microcurie per cc. of theglass or silica gel. In the absence of malfunction requiring overhaul ofthe other parts of the radwaste treatment system, 100 or less to 10⁹ ormore, preferably 100 to 10⁶, weight parts of radwaste can be treated foreach weight part of porous silicate glass or silica gel havingsilicon-bonded alkali metal oxy, Group Ib metal oxy and/or ammonium oxygroups pursuant to this invention.

EXAMPLE 29

A molten glass having the composition described in Example 1 wasproduced by heating said composition in a platinum crucible up to 1400°C. in an electric furnace. The molten glass is then pulled to form rodsabout 8 mm in diameter and about 2.5 cm long. After cooling the glassrods were phase-separated by heat treating at 550° C. for 110 minutesand then were crushed and sieved through a 32 mesh screen onto a 150mesh screen. The glass particles collected on the 150 mesh screen wereleached in 3N HCl at 50° C. for 6 hours and then were rinsed indeionized water until the rinse water reached a pH of about 7.

Two solutions were prepared as follows:

Solution 1 was a 0.5M NaOH aqueous solution made from 2 grams sodiumhydroxide and 100 ml water and had a pH of greater than 13.

Solution 2 was 0.5M sodium nitrate aqueous solution and was made from4.3 grams sodium nitrate, 25 ml ammonium hydroxide and 75 ml water andhad a pH of about 12.1.

The particulate porous glass produced as described above were dividedinto four portions and the portions were treated as follows:

Portion 1 was allowed to remain in pure water.

Portion 2 was immersed in solution 1.

Portion 3 was immersed in solution 1.

Portion 4 was immersed in solution 2.

After two hours, portions 2, 3 and 4 were rinsed until the rinse waterbecome neutral, i.e., reached a pH of about 7. Portion 2 was thenimmersed in 3N HCl for two hours followed by rinsing until neutral.Portions 2 and 3 were thus treated by the procedure described in U.S.Pat. No. 3,549,524 (col. 4, lines 65-75) for removing colloidal silicaprecipitate from the pores of porous glass. Portion 2 followed thedirections of the patent which called for immersion in aqueoushydrochloric acid whereas portion 3 did not include the hydrochloricacid immersion.

All four portions were dried and analyzed by atomic absorptionspectroscopy for sodium content. The analytical results are given inTable 5 below.

                  TABLE 5                                                         ______________________________________                                        Portion No.                                                                           Na (ppm)   Na.sub.2 O (ppm)                                                                         Mol % Na Cation                                 ______________________________________                                        1       202        272        0.054                                           2       510        687        0.136                                           3       720        990        0.198                                           4       14,800     19,900     3.98                                            ______________________________________                                    

This example illustrates the ease of introducing the silicon-bondedsodium oxy groups using the buffering techniques exemplified by solution2. It also illustrates that a sufficient amount of such groups can bereadily obtained by the buffering techniques whereas extra precautionsshould be taken in the formation of such groups with the unbufferedalkali metal hydroxide in order to provide a sufficient level of suchgroups without undue attack on the porous glass. The proportions ofsilicon-bonded sodium oxy groups provided by portions 1, 2 and 3 areinadequate to provide a substantial amount of cation exchange withradioactive cations in the present invention.

EXAMPLE 30

Five aqueous sodium hydroxide solutions were prepared as identified inTable 6 below which lists the concentration and pH of each.

                  TABLE 6                                                         ______________________________________                                        Solution No.   Concentration (M)                                                                           pH                                               ______________________________________                                        A              0.001         11                                               B              0.01          12                                               C              0.1           13                                               D              1.0           14                                               E              3.0           14                                               ______________________________________                                    

Ten porous glass rods were produced as described in Example 1. Pairs ofglass rods were immersed in each of the five solutions. Periodically onerod of the immersed glass rods was removed from each solution and wasanalyzed after rinsing until the rinse water became approximatelyneutral. Before analysis, the samples were dried and then analyzed byatomic absorption spectroscopy for sodium content. The analyticalresults are given in Table 7 below.

                  TABLE 7                                                         ______________________________________                                        Amount of Na.sup.+  Bound to Porous Glass                                     A             B         C                                                     Immersion      Mol         Mol       Mol                                      Time (Hrs.)                                                                           ppm    %      ppm  %    ppm  %    D    E                              ______________________________________                                        22      --     --     --   --   --   --   77%                                                                           dissolved                           24      233           1800      4833      Completely                                                                    dissolved                            48*    309           2056      7020      --                                  ______________________________________                                         *May contain some unbound Na.sup.+  due to incomplete rinsing before          analysis.                                                                

This example, as regards solution C, illustrates the technique forproducing porous silicate glass containing effective proportions ofsodium cation bonded through oxy linkages to silicon by immersion inaqueous sodium hydroxide of a suitable concentration and for a suitableperiod of immersion.

Solution B provides porportions of silicon-bonded sodium oxy groups thatare on the low side but, nevertheless might find use in certainapplications of the present invention.

Solutions D and E obviously attacked the porous glass and resulted incomplete dissolution thereof within 24 hours immersion time.

Solution A even after 48 hours was ineffective in providing sufficientsodium cations bonded to silicon through oxy linkages. This exampleillustrates that one skilled in the art utilizing proper controls canproduce suitable cation exchange porous glass forms useful in thisinvention by unbuffered alkali metal hydroxide immersion techniques.

EXAMPLES 31 AND 32

Porous glass rods having silicon-bonded sodium oxy groups were producedby the procedures described in Examples 22 and 23 and were immersed inan aqueous solution of neodynium nitrate which was stirred at about 25°C. for about 22 hours. Periodically samples of the solution werewithdrawn and analyzed. The results are given in Table 8 below andillustrate the efficiency of the porous glass in removing neodyniumcations from aqueous solution pursuant to this invention.

                  TABLE 8                                                         ______________________________________                                        Time         Nd.sup.3+ Na.sup.+  (ppb)                                        ______________________________________                                        0            25,700    0-100                                                  1/4          13,400    --                                                     1             5,800    --                                                     2             1,500    --                                                     22            1,000*   32,000                                                 ______________________________________                                         *below the measuring capacity of the analytical procedure used.          

In Example 32, the porous glass resulting from the above-describedExample 31 was heated to collapse the pores.

EXAMPLES 33 AND 34

Two porous glass rods one inch and a half long each, were prepared aspreviously described to contain about 1.5 wt. % sodium cations bonded tosilicon through oxy groups. One of the rods was immersed in 80 ml of asolution containing 25 ppm cupric cation made from 6.7 milligram ofCuCl₂.2H₂ O in 100 ml aqueous solutions. Initially, the cupric ioncontent of the solution was measured and found to be 22.3 ppm and thesodium ion content was found to be 0.09 ppm. After four hours immersionthe cupric cation content was measured and found to be 2.2 ppm and thesodium cation content was found to be 18.4 ppm illustrating that thecupric cation exchanged with the sodium cation.

The second porous glass rod was immersed in a solution containingnominally 10 ppm Sr²⁺ made from 3.04 milligram SrCl₂.6H₂ O in a 100 mlaqueous solution. Initially, the Sr²⁺ content of the solution wasmeasured and found to be 10.7 and the sodium content was 0.302. Afterfour hours immersion, the Sr²⁺ content had dropped to 0.149 ppm and thesodium cation content had increased to 17.1 ppm.

EXAMPLES 35, 36 AND 37

Three one inch long porous glass rods prepared as described in Example1, were immersed in one of the three solutions as described below. InExample 35, the rod was immersed for 115 hours at 25° C. in a solutionmade from 10.4 g lithium nitrate, 12 ml aqueous ammonium hydroxide and38 ml of water. In Example 36, the solution was made from 8.5 g ofsilver nitrate, 25 ml aqueous ammonium hydroxide and 74 ml H₂ O and theimmersion was 66 hours at 25° C. In Example 37, the solution was madefrom 8.5 g CuCl₂.2H₂ O 25 ml aqueous ammonium hydroxide and 75 ml ofwater and the immersion time was 66 hours at 25° C. All rods were thenthoroughly rinsed and each was immersed in a separate 10 ppm Sr²⁺solution made from Sr(NO₃)₂. In Example 35, the initial Sr²⁺ content wasmeasured and found to be 9.65 ppm and after six hours immersion it wasfound to be 0.009 ppm while the lithium ion content after six hoursimmersion was found to be 7.77. In Example 36, the initial Sr²⁺ contentwas measured and found to be 9.65 ppm and after six hours immersion ishad dropped to 0.079 ppm while the silver ion content of the solutionafter six hours increased to 82 ppm. In Example 37, the initial Sr²⁺content was measured and found to be 9.65 ppm and after six hoursimmersion, it had dropped to 0.07 ppm while the cupric ion content aftersix hours immersion was found to be 0.137 ppm. The disappearance of Sr²⁺ions from the solution in Example 37 without concomitant appearance ofsubstantial amounts of cupric ion suggests that silicon-bonded ammoiniumoxy groups first cation-exchanged with the Sr²⁺ ions and then when moreSr²⁺ ions are added to the immersion solution, cupric cations will beexchanged from the glass and then begin to appear in substantial amountsin the immersion solution.

EXAMPLES 38 AND 39

One one inch long porous glass rod prepared as described in Example 1was immersed in a solution made from 8.5 g CuCl₂.2H₂ O, 25 ml aqueousammonium hydroxide and 74 ml H₂ O for 66 hours at 25° C. In Example 39,an identical porous glass rod was immersed in a solution made from 30 gsodium nitrate, 25 ml aqueous ammonium hydroxide and 75 ml water forthree days at 25° C. Each rod was then immersed in a 500 ppm Sr²⁺solution prepared from 0.6 g stronium nitrate and 500 ml of water. InExample 38, the initial Sr²⁺ content was measured and was found to be460 ppm and after four hours immersion it had dropped to 380 ppm andafter 49 hours immersion it had dropped to 119 ppm. In Example 39, theinitial Sr²⁺ was measured and found to be 470 ppm and it dropped to 340ppm after four hours immersion.

EXAMPLES 40 AND 41

Two one inch long porous glass rods each having a surface area of about8.3 cm², prepared in a manner similar to that given in Example 1 wereimmersed in the following aqueous solutions: In Example 40, theimmersion was for 115 hours in a solution of 10.4 g lithium nitrate, 12ml aqueous ammonium hydroxide and 38 ml water. In Example 41, theimmersion was for three days in a solution of 30 g sodium nitrate, 25 mlammonium hydroxide and 75 ml of water. After immersion in each example,the glass rods were thoroughly rinsed with water and immersed in anominally 100 ppm Sr²⁺ solution made by mixing 20 ml of the 500 ppm Sr²⁺solution described in Examples 38 and 39 with 80 ml of water. In Example40, the initial Sr²⁺ content was measured and found to be about 93 andafter four hours immersion, it was found to have dropped to about 23. InExample 41, the initial Sr²⁺ content was measured and found to be 93 andafter four hours immersion it had dropped to 13.

For reasons of safety all simulated radwaste solutions used in theExamples were actually non-radioactive; however, radioactive solutionsof the same kind can be substituted and concentrated and encapsulated inaccordance with the foregoing Examples.

EXAMPLE 42

This example illustrates a method for treating primary coolant from apressurized nuclear reactor plant. A mixture of powders of silica, boricacid, sodium carbonate and potassium carbonate is prepared in suchproportions that yield a glass comprising 3.5 mol percent Na₂ O, 3.5 molpercent K₂ O, 33 mol percent B₂ O₃ and 60 mol percent SiO₂. The mixtureis heated in a platinum crucible up to 1400° C. in an electric furnaceto produce a molten glass which is pulled into rods about 8 mm dia andabout 25 cm long. The glass rods are cooled and the glass is phaseseparated by heat-treating at about 550° C. for 110 minutes. The rodsare then crushed to form a powder which is sieved through a 32 meshscreen onto a 150 mesh screen. The glass particles collected on the 150mesh screen are leached in 3N HCl at about 50° C. for about 6 hours toremove the boronrich phase and leave behind a porous glass comprisingabout 95 mol percent SiO₂ and about 5 mol percent B₂ O₃. The porousglass has interconnected pores and contains at least about 5 mol percentsilicon-bonded hydroxyl groups. The glass particles are then rinsed indeionized water until the rinse water reaches a pH of about 7.

The porous glass powder is then immersed in an approximate 3.2 molarlithium nitrate-ammonium hydroxide (1 part ammonium hydroxide to 3 partswater) aqueous solution for six hours and then is rinsed in water untilthe pH of the rinse water is reduced to about 8. The resulting powder isthen placed in an ion exchange column made of the Vycor glass asdescribed in Examples 20 and 21. A radioactive primary coolant from apressurized water nuclear reactor plant utilizing UO₂ fuel clad instainless steel (containing 4.9 weight percent ²³⁵ U) is passed throughthe column. The primary coolant has a composition of 100 ppm Boron, 1ppm ⁷ Lithium, approximately 100 ppb Silica, and the radionucleideslisted in Table 4. Table 4 lists the radionuclide, the probable source,the probable form and the average concentration in microcuries permilliliter. The cationic radionuclides ion-exchange with the lithiumcations bonded to silicon through oxy groups in the porous silicateglass powder thereby binding the radionuclides to the porous glassthrough said silicon-bonded oxy groups and releasing lithium cations tothe coolant solution. The insoluble radioactive solids in the coolantalso filter out on the external surfaces of the porous glass particles.Additional porous glass particles can be added to increase the filteringcapacity of the ion exchange column as the insoluble solids build-up inthe column. Under some conditions, mainly dependent on existinggovernmental regulations, the porous silicate glass containing boundcationic radionuclides may be disposed and/or buried or suitablycontainerized often times in steel and/or concrete or mixed with cementpowder or urea-formaldehyde formulations and "set" therein andthereafter disposed and/or buried. The particulate porous glass can alsobe heated to collapse the pores thereof as described herein.

The anionic radionuclides are not substantially removed in the columnand pass with the coolant through the column. The anionic radionuclidescan be subsequently removed by treatment with conventional anionicexchange resins. Upon regeneration of the conventional anion exchangeresin after it becomes loaded, the regenerant solution containing theanionic radionuclides can be concentrated by evaporation and theresulting concentrate can be molecularly stuffed into the pores of theporous glass in the ion exchange column after said porous glass hadbecome substantially loaded with silicon-bonded radionuclide cation oxygroups. It is preferred to first dry the loaded porous glass so that theanionic radionuclide concentrate can readily enter the pores of theporous glass. The anionic radionuclides can be precipitated or depositedwithin the pores of the porous glass. The anionic radionuclides can beprecipitated or deposited within the pores of the porous glass by thecareful drying procedures disclosed in U.S. Pat. No. 4,110,096.Thereafter, the porous glass particles can be heated to collapse thepores thereof. Thereafter, if desired the column can be heated tocollapse the Vycor glass around the particles thereby enveloping thefiltered solids and the glass particles containing the cationic andanionic radionuclides within the Vycor glass column. While the glasscolumn cracks because of differential thermal contraction it stillcontains and further immobilizes the radioactive materials and forms aproduct that is many times more durable than cement or metal drumsheretofore used. There is thus provided a durable package ofconcentrated radionuclides which is highly resistant to leaching bywater or other fluids.

EXAMPLE 43

This example illustrates the ability to reduce radioactive ionconcentrations down to levels as low as 0.01 ppt (i.e., ˜10⁻¹⁴ g/g). Aporous rod, 2.5 cm long and 8 mm. in diameter, prepared in the mannerdescribed in Example 1 was subjected to a primary ion exchange byimmersing it in a solution of 30 g NaNO₃ and 100 ml NH₄ OH for 3 days at20° C. The resulting impregnated rod was then washed in deionized wateruntil the rinse water has a pH of about 8. It was then soaked in astirred secondary solution containing radioactive Sr⁹⁰ which is preparedas follows. One-hundred microcuries of carrier-free Sr⁹⁰ inapproximately 2/3 ml of 0.5 NaCl purchased from New England NuclearCorporation was diluted to 100 ml (1 μCi/ml) with demineralized water.An aliquot of this solution was further diluted to prepare a 50 mlsoaking solution with a Sr⁹⁰ concentration of 80 nCi/ml. The soakingsolution was then equilibrated by stirring for 20 hours in a 100 ml PTFEbeaker at 28° C. The soak solution pH was measured to be 7.0. Afterequilibration, the porous glass rod was introduced into the solution andsoaked for approximately 26 hours. Measurements of the Sr⁹⁰ and Y⁹⁰concentrations were taken before adding the porous glass rod and atvarious intervals after soaking begins. The Sr⁹⁰ and Y⁹⁰ concentrationin the solution were determined by measuring the β-activity of planchetsmade by evaporating a 0.1 ml aliquot of the solution from a clean copperdisc 1 in. in diameter by 0.022 in. thick. The solution was thus sampledevery 40 minutes for the first 12 hours.

Each sample was counted sequentially with two background and twostandardization planchets to permit compensation for long term drift inthe detector response. Each count was first corrected for the detectorresolving time, then the sample counts were normalized to the standardsand backgrounds were subtracted to obtain normalized net count rates.

In order to separate the Sr-90 and Y-90 behavior, the well known Batemanequations were used to relate the quantities of the individual membersof a radioactive decay chain. For Sr/Y-90 the chain takes the simpleform: ##EQU1## where A, B and C are the quantities of Sr-90, Y-90 andZr-90. The quantities of A and B present at any time t are given by##EQU2## where λ_(A) and λ_(B) are the reciprocal time constants for thedecay of Sr-90 and Y-90 respectively and A_(o) and B_(o) are the initialconcentrations respectively. The detector response (Σ) (net ofbackground and corrected for resolving time) to a sample containing anunknown mixture of the two radioactive nuclides is

    Σ=D.sub.A +D.sub.B                                   (3)

where ##EQU3## where n_(A) and n_(B) are the counting efficiencies ofSr-90 and Y-90 respectively. If the sample is counted at two differenttimes, Eq. (3) yields a pair of simultaneous equations in A_(o) andB_(o), the quantities of the two isotopes present at time t_(o).

To determine n_(A) and n_(B) for use in Eq. 4 the following procedurewas used. The average efficiency ##EQU4## of the detector for the betaparticles from a mixture of Sr-90 and Y-90 was determined to be 0.33172.The calculated Sr-90 activity n_(A), is essentially independent ofn_(B). The exact value of n_(B) was not known but from other detectorcalibrations n_(A) /n_(B) should lie between 0.5 and 0.8. Since aprecise n_(B) was not crucial for an adequate understanding the dataf=0.6 was chosen.

The results of the experiment were as follows.

A. Mass Concentration. The mass concentration of an isotope in solutionis obtained by dividing the activity concentration by the specificactivity (141 Ci/g for Sr-90 and 5.44×10⁵ Ci/g for Y-90) and by thesolution density (essentially unity). Table 9 and FIGS. 1 and 2 show themass concentration in the solution vs. time for Sr-90 and Y-90,respectively.

The Sr-90 mass concentration decreased approximately exponentially forabout 6 h, followed by a transition to equilibrium. At 18 h theconcentration was 10% above equilibrium and the transition appeared tobe complete when the final datum was taken at 26.5 h. The Y-90 massconcentration decreased approximately exponentially for about 3 h,followed by transition to what appears to be equilibrium.

B. Concentration Reduction. The concentration of strontium in solutionwas reduced from 1.3×10⁻⁹ g/g to 1.9×10⁻¹² g/g, a reduction by a factorof 693. The concentration of yttrium in solution was reduced from3.2×10⁻¹² g/g to 2.3×10⁻¹⁴ g/g, a reduction by a factor of 137.

                  TABLE 9                                                         ______________________________________                                        REDUCTION IN CATION CONCENTRATION                                             (Sr.sup.90 AND Y.sup.90) OF SOLUTION BY A SODIUM DOPED                        POROUS GLASS PHASIL ROD USED FOR ION                                          EXCHANGE.                                                                              Sr.sup.90                                                                     CONCENTRATION  Y.sup.90 CONCENTRATION                                SOAK TIME                                                                              IN SOLUTION    IN SOLUTION                                           (hours)  (10.sup.-6 g/g sol)                                                                          (10.sup.-13 g/g sol)                                  ______________________________________                                        0        1.3            3.2                                                   0.7      0.9            2.2                                                   1.4      0.54           1.2                                                   2.0      0.32           0.56                                                  2.7      0.185          0.40                                                  3.4      0.10           0.35                                                  4.0      0.055          0.27                                                  4.7      .034           0.25                                                  5.4      .0185          0.25                                                  5.6      .0150          0.26                                                  6.0      .012           0.25                                                  6.6      .0076          0.24                                                  7.4      .0058          0.24                                                  8.0      .0041          0.25                                                  8.6      .0057          0.32                                                  9.4      .0037          0.23                                                  10       .0031          0.39                                                  10.6     .0032          0.22                                                  11.4     .0028          0.22                                                  12.0     .0032          0.23                                                  26.6     .0019          0.23                                                  ______________________________________                                    

EXAMPLE 44

A particulate porous glass, prepared as in Example 1, except thatbetween heat treatment and leaching the rods were mechanically crushedand the powder was sieved. The resulting porous glass powder withsilicon bonded hydroxyl groups on the pore surface, is soaked in asolution of 30 g NaNO₃, 25 ml NH₄ CH and 75 ml water at 20° C. for 3hours to allow Na⁺ ions to exchange for protons from the silicon-bondedhydroxyl groups on the glass surface. The resulting Na powder then fillsa polypropylene column of cross-section 3.8 cm² up to a height of 10.5cm. The column support for the glass is a 10 μm polypropylene filterdisc. The head height is measured from the top of the glass in thecolumn to the midpoint of the feed solution container. All tests wereconducted with head height of 95.3 cm of water. Two runs were made usinga size of 0.710-0.355 mm for the glass powder. The results aresummarized:

    ______________________________________                                             Flow                                                                          Rate              Vol    Sr     Na     Si                                     (cm.sup.3 /                                                                           Feed Soln effluent                                                                             removed                                                                              released                                                                             lost                              Run  min)    [Sr] (ppm)                                                                              (cm.sup.3)                                                                           (g)    (g)    (g)                               ______________________________________                                        1     18      20       3867   .0773  .111   .03                               2    180     100       5685   .36    .18    .03                               ______________________________________                                    

For run 2 the Na:Sr atom-atom ratio is 2:1 and for run 1 it is 5.6:1.The high value for run 1 may be due to incomplete washing of the glass.The Si release produced an average concentration of 3-5 ppm in theeffluent. For run 1, after 4 hours and 46 minutes, there was no sign ofbreak-through. The maximum Sr concentration in the effluent being 0.005and 0.013 ppm respectively with average concentrations of 0.003 and0.005 ppm.

Run 2 began to show signs of breakthrough after ˜1000 cm³ of solutionwere passed and for this reason is most useful in calculating columncharacteristics. If we assume that almost all of the capacity of thecolumn was exhausted by the end of the experiment the total capacity canbe calculated as ##EQU5##

In conclusion starting with a Sr concentration of 20 ppm the glasscolumn used in runs 1 and 2 show initial leakage rates of 103 ppb andaverage leakage rates of 3-5 ppb.

What is claimed is:
 1. Process which causes the proton (H⁺) ofsilicon-bonded hydroxyl groups on the internal surfaces of poroussilicate glass to undergo ion-exchange reaction without occurrence ofsubstantial dissolution of the glass during the reaction whichcomprises:(a) impregnating a porous silicate glass characterized by atleast 75 mol percent SiO₂, an interconnecting pore structure, andsilicon-bonded hydroxyl groups on its surfaces, (b) with a liquidcontaining non-radioactive alkali metal cations, non-radioactive GroupI(b) metal cations, ammonium cations, or mixtures thereof, (c) saidliquid buffered with non-radioactive ammonium cations to maintain a pHin the range of about 11 to about 13, (d) for a period of time toprovide a distribution of said non-radioactive cations within theinterconnected pores of said glass, said cations being bonded to siliconthrough divalent oxy groups.
 2. The process of claim 1 wherein saidion-exchanged porous glass contains at least about 0.3 mol percent toabout 10 mol percent alkali metal cations bonded to silicon throughdivalent oxy groups.
 3. The process of claim 1 or 2 wherein potassiumcation is bonded to surface silicon through divalent oxy groups.
 4. Theprocess of claim 1 or 2 wherein sodium cation is bonded to surfacesilicon through divalent oxy groups.
 5. The process which comprisesreacting the ion-exchange porous silicate glass containing bondednon-radioactive cations defined in claim 1 or 2 with a liquid containingtoxic cations, said toxic cations being capable of displacing saidnon-radioactive cations to provide a distribution of internal surfacesilicon-bonded toxic cation oxide groups within the pores of said glass;and thereafter confining the resultant porous silicate glasscharacterized by such internal silicon-bonded toxic cation oxide groups.6. The process of claim 5 wherein the confinement of said resultantporous silicate glass is effected by heating to collapse said porescontaining such internal silicon-bonded toxic cation oxide groups. 7.The process of claim 5 which comprises impregnating the ion-exchangedporous silicate glass which contains bonded non-radioactive cations asdefined in claim 1 or 2 with a liquid having a pH in the range of fromabout 2 to about 13 and containing radioactive cations, for a period oftime to dispose said liquid within the pores of said glass and todisplace at least a portion of said non-radioactive cations by saidradioactive cations to provide a distribution of internal surfacesilicon-bonded radioactive cation oxy groups disposed within the poresof said glass; and thereafter confining the resultant porous silicateglass characterized by such internal silicon-bonded radioactive cationoxy groups.
 8. The process of claim 7 wherein said ion-exchanged poroussilicate glass contains non-radioactive alkali metal cations bonded tosilicon through divalent oxygen linkages on the internal surfaces ofsaid pores of the glass.
 9. The process of claim 7 wherein from about0.3 mol percent to about 10 mol percent non-radioactive sodium cation isbonded to said silicon.
 10. Process of claim 9 wherein the resultantporous silicate glass contains at least one part per billion by weightof radioactive cation bonded to silicon through divalent oxygenlinkages.
 11. Process of claim 7 wherein said liquid is an aqueousmedium comprising a mixture of radioactive cations selected from thegroup consisting of radioactive cations of rubidium, strontium, thelanthanides, cobalt, cadmium, zironium, molybdenum, technetium, niobium,ruthenium, palladium, tellurium, cesium, barium, francium, yttrium,radium, the actinides, and mixtures thereof; wherein the amount of saidnon-radioactive cations in said porous silicate glass is about 0.3 molpercent to about 10 mol percent; and wherein said pH is in the range offrom about 6 to about 9.5.
 12. A process for removing radioactivecations from a liquid stream of radioactive nuclear wastes containingthe same and concentrating said radioactive cations comprisingimpregnating an ion-exchanged porous silicate glass which containsbonded non-radioactive cations defined in claim 1 or 2, with a liquidstream of radioactive nuclear wastes containing radioactive cations fora period of time sufficient to dispose said liquid within the pores ofsaid glass and to displace said non-radioactive cations to provide adistribution of internal silicon-bonded radioactive cation oxide groups;and thereafter confining the resultant porous silicate glasscharacterized by such internal silicon-bonded radioactive cation oxidegroups.
 13. Process of claim 12 wherein said liquid containingradioactive cations has a radioactivity of about 0.01 microcurie toabout 1 microcurie per milliliter.
 14. A process which comprisesimpregnating a porous silicate glass or silica gel having interconnectedpores and non-radioactive protons (H⁺) bonded to silicon throughdivalent oxygen linkages on the internal surfaces of said pores, withprimary coolant water of a boiling water reactor system which containsradioactive cations to dispose said primary coolant water within thepores of said glass or silica gel after adding ammonium hydroxide tosaid primary collant water to both maintain the pH thereof in the rangeof about 6 to about 9.5 and to effect the ion-exchange of saidnon-radioactive protons with ammonium cations, said non-radioactiveammonium cations being capable of being displaced by said radioactivecations to provide a distribution of internal silicon-bonded radioactivecation oxy groups within the pores of said glass or silica gel; andthereafter confining the resultant porous silicate glass or silica gelcharacterized by such internal silicon-bonded radioactive cation oxygroups.
 15. Process of claim 14 wherein said pH is maintained in therange of from above 7 to about
 9. 16. The ion-exchanged porous silicateglass product of claim
 1. 17. The ion-exchanged porous silicate glassproduct of claim
 2. 18. The ion-exchanged porous silicate glass productof claim 1 or 2 wherein said alkali metal cation is potassium bonded tosurface silicon through divalent oxy groups.
 19. The ion-exchangedporous silicate glass product of claim 1 or 2 wherein said alkali metalis sodium bonded to surface silicon through divalent oxy groups.
 20. Anion-exchange column comprising the ion-exchanged porous silicate glassproduct of claim 16 or 17 as ion-exchange medium therefor.
 21. Anion-exchange column comprising the ion-exchanged porous silicate glassproduct of claim 19 as ion-exchanged medium therefor.
 22. Poroussilicate glass prepared as defined in claim 1 and containing at leastone part per billion by weight of radioactive cation of the groupconsisting of radioactive cations of rubidium, strontium, thelanthanides, cobalt, cadmium, zirconium, molybdenum, technetium,niobium, ruthenium, palladium, tellurium, cesium, barium, francium,yttrium, radium, the actinides, and mixtures thereof; said radioactivecation bonded to surface silicon through divalent oxygen linkages. 23.Porous silicate glass of at least 75 mol percent SiO₂, an interconnectedpore structure, a surface to weight ratio of from about 5 to about 1500m² /g, and containing non-radioactive ammonium cations disposed withinthe interconnecting pores and bonded to surface silicon thereof throughdivalent oxy linkages.
 24. The porous silicate glass of claim 23 which,in addition to ammonium cations, contains non-radioactive cations of thegroup consisting of alkali-metal cations, Group I(b) cations andmixtures thereof, bonded to said surface silicon.
 25. The poroussilicate glass of claim 24 characterized by a surface to weight ratio atleast upward of 100 m² /g and ammonium and sodium cations bonded to saidsurface silicon.
 26. The porous silicate glass of claim 23 or 24 or 25characterized by about 0.3 to about 10 mol percent cations.
 27. Theporous silicate glass of claims 24 or 25 characterized by about 1 toabout 10 mol percent cations.
 28. The porous silicate glass of claims 23or 24 or 25 in particulate form.
 29. An ion-exchange column comprisingparticulate porous silicate glass as defined in claims 23 or 24 or 25.30. Porous silicate glass characterized by at least 75 mol percent SiO₂,an interconnecting pore structure, a surface to weight ratio of fromabout 5 to about 1500 m² /g, and radioactive cations, disposed withinthe interconnecting pores and bonded to surface silicon through divalentoxy linkages, said radioactive cations of the group consiting ofradioactive cations of rubidium, strontium, the lanthanides, cobalt,cadmium, zirconium, molybdenum, technetium, niobium, ruthenium,palladium, tellurium, cesium, barium, francium, yttrium, radium, theactinides, and mixtures thereof; said radioactive cation bonded tosilicon through divalent oxygen linkages.